Method for producing optical compensating film, optical compensating film circularly polarizing plate, and liquid crystal display

ABSTRACT

Provided are a method for producing an optical compensating film, which comprises stretching a cellulose acetate film, the cellulose acetate film having a water content of 2.0 to 20.0% by weight, wherein the cellulose acetate for the film has an acetyl value of from 57.0% to 62.5%; the optical compensating film produced according to the method for producing an optical compensating film; a polarizing plate that is laminate including the optical compensating film and a polarizing film; and an image display that comprises at least one of the optical compensating film and the polarizing plate. According to the method for producing an optical compensating film of the invention, optical compensating films having a large NZ factor and having good view angle characteristics (especially λ/4 plates having a phase difference of λ/4 in a broad wavelength range), can be stably produced on an industrial scale. In particular, in the method, the NZ factor of the optical compensating films produced can be well controlled, without changing the retardation thereof, and therefore the method ensures industrial-scale stable production of optical compensating films having improved view angle characteristics. In addition, image displays, especially reflection or semi-transmission liquid crystal displays and organic electroluminescent device-having image displays that comprise the optical compensating film produced according to the method of the invention or comprise a polarizing plate having the optical compensating film all have good view angle characteristics.

TECHNICAL FIELD

[0001] The present invention relates to a method for producing anoptical compensating film (especially λ/4 plate) of cellulose acetate.Further, the invention relates to the optical compensating film producedin the method, and to an image display comprising it (e.g., reflectionor semi-transmission liquid crystal display, organic electroluminescent(EL) device-having display).

BACKGROUND ART

[0002] A liquid crystal display generally comprises at least a liquidcrystal cell, a polarizing plate and an optical compensating sheet(phase retarder plate). Concretely, a transmission liquid crystaldisplay comprises two polarizing plates disposed on both sides of aliquid crystal cell therein, and one or two optical compensating sheetssandwiched between the liquid crystal cell and the polarizing plate. Areflection liquid crystal display comprises a reflector, a liquidcrystal cell, one optical compensating sheet and one polarizing platethat are arrayed in that order.

[0003] The liquid crystal cell in such displays generally comprises rodliquid-crystalline molecules, two substrates for sealing up them, and anelectrode layer for applying voltage to the rod liquid-crystallinemolecules. Various display modes of liquid crystal cells are proposed,depending on the difference in orientation of the rod liquid-crystallinemolecules in the cells. For example, TN (twisted nematic)-mode cells,IPS (in-plane switching)-mode cells, FLC (ferroelectric liquidcrystal)-mode cells, OCB (optically compensatory bend)-mode cells, STN(super twisted nematic)-mode cells and VA (vertically aligned)-modecells are for transmission displays; and HAN (hybrid alignednematic)-mode cells are for reflection displays.

[0004] The polarizing plate generally comprises a polarizing film and atransparent protective film, and the polarizing film is generallyprepared by dipping a polyvinyl alcohol film in an aqueous solution ofiodine or dichromatic dye followed by monoaxially stretching thethus-dipped film. Two transparent protective film are attached to bothsides of the polarizing film to construct the polarizing plate.

[0005] Optical compensating sheets are used in various liquid crystaldisplays for solving a problem of image discoloration and for enlargingthe field of view.

[0006] Of those, λ/4 plates have many applications, for example, foroptical compensating films for liquid crystal displays, andantireflection films for organic EL displays, and they are now inpractical use. However, many λ/4 plates heretofore used in the artattain λ/4 or λ/2 only in a specific wavelength range.

[0007] JP-A 27118/1993 and 27119/1993 disclose an optical compensatingfilm fabricated by laminating a birefringent film of large retardationand a birefringent film of small retardation in such a manner that theiroptical axes cross each other at right angles. The compensating filmcould theoretically function as a λ/4 plate in the overall range ofvisible light, so far as the difference in retardation between thelaminated two films is λ/4 in the overall range of visible light. JP-A68816/1998 discloses an optical compensating film capable of attainingλ/4 in a broad wavelength range, which is fabricated by laminating apolymer film of λ/4 in a specific wavelength range and a polymer film ofλ/2 of the same material in the same wavelength range as that of theformer. JP-A 90521/1998 also discloses an optical compensating filmfabricated by laminating two polymer films and capable of attaining λ/4in a broad wavelength range. However, the optical compensating film ofthe type fabricated by laminating two films has various problems in thatit is thick and its cost is high. Therefore, an optical compensatingfilm of a single film that realizes λ/4 in a broad wavelength range isdesired.

[0008] In this connection, JP-A 2006-137116 and WO 00/65384 have adescription relating to an optical compensating film of a single polymerfilm of which the phase retarder reduces in a shorter wavelength range,and to its application to circularly polarizing plates and reflectionliquid crystal displays. As the parameter of controlling the view anglecharacteristic of the above-mentioned λ/4 plate, employed is a numericalvalue defined by (nx−nz)/(nx−ny) (this is hereinafter referred to as anNZ factor). nx, ny and nz indicate the refractive index along the slowaxis in plain (the maximum refractive index in plain) of the phaseretarder, the refractive index perpendicular to the slow axis in planeof the phase retarder, and the refractive index along the thicknessdirection, respectively. WO 00/65384 says that the preferred range ofthe NZ factor is 1≦NZ≦2.

[0009] Preferably, the NZ factor is controllable. This is because, in aliquid crystal display for image formation, the birefringence (Δn) ofthe liquid crystal cell varies depending on the liquid crystal paneltherein and the angle-dependency of Δn also varies depending on theliquid crystal panel. Therefore, if the NZ factor of the opticalcompensating film in the display is controllable, the view anglecharacteristic of the display can be optimized, requiring no change ofthe retardation value Re of the film.

[0010] However, the NZ factor is defined by the refractive indices inthree directions of the film, and is therefore correlated with the drawratio of the film. Concretely, when the draw ratio of the film in themachine direction increases more and therefore the film is most likelyin monoaxial orientation, then the NZ factor of the film comes nearer to1 from a larger value. In case where a λ/4 plate is fabricated accordingto the width-unlimited monoaxial stretching method described in theExamples in WO 00/65384, the draw ratio of the film that realizes aretardation of λ/4 is determined by the elongation at break of the film,and therefore the NZ factor of the film shall be indiscriminatelydetermined.

DISCLOSURE OF THE INVENTION

[0011] One object of the present invention is to provide a method forproducing an optical compensating film (especially, a λ/4 plate thatattains a phase shift of λ/4 in a broad wavelength range), of which cancontrol NZ factor without a retardation change in the film, and whichhas a good view angle characteristic, and to provide such an opticalcompensating film having the advantages as above.

[0012] Another object of the invention is to provide a polarizing platethat comprises the optical compensating film as above and has a goodview angle characteristic, and to provide an image display device(especially, a reflection or semi-transmission liquid crystal display,and an organic electroluminescent (EL) device-having display) thatcomprises the optical compensating film or the polarizing plate asabove.

[0013] According to the invention, there are provided a method forproducing an optical compensating film, an optical compensating film, apolarizing plate, and a liquid crystal display mentioned below, whichattain the above-mentioned objects of the invention.

[0014] 1. A method for producing an optical compensating film, whichcomprises stretching a cellulose acetate film, the cellulose acetatefilm having a water content of 2.0 to 20.0% by weight,

[0015] wherein the cellulose acetate for the film has an acetyl value offrom 57.0% to 62.5%.

[0016] 2. The method for producing an optical compensating film asdescribed in above 1, wherein the optical compensating film has aretardation value measured at a wavelength of 550 nm (Re550) of 20 nm to2000 nm: 20 nm≦Re550≦2000 nm.

[0017] 3. The method for producing an optical compensating film asdescribed in above 1 or 2, wherein the optical compensating film has adistribution of the retardation value measured at a wavelength of 550 nm(Re550) of 10% or less in both a width direction and a longitudinaldirection of the film.

[0018] 4. The method for producing an optical compensating film asdescribed in any of above 1 to 3, wherein the optical compensating filmhas:

[0019] the retardation value measured at a wavelength of 450 nm (Re450)of 60 to 135 nm; and

[0020] the retardation value measured at a wavelength of 590 nm (Re590)of 100 to 170 nm, and the stretched film satisfies the condition:(Re590−Re450)≧2 nm.

[0021] 5. The method for producing an optical compensating film asdescribed in any of above 1 to 4, wherein the optical compensating filmsatisfies the conditions: 0.5<Re450/Re550<0.98; and1.01<Re650/Re550<1.35, in which Re450, Re550 and Re650 represent theretardation values measured at a wavelength of 450 nm, 550 nm and 650nm, respectively.

[0022] 6. The method for producing an optical compensating film asdescribed in any of above 1 to 5, wherein the cellulose acetate film isdipped in water and/or exposed to water vapor to absorb water, beforethe stretch.

[0023] 7. The method for producing an optical compensating film asdescribed in any of above 1 to 6, wherein no water film is substantiallyformed on the surface of the cellulose acetate film when the celluloseacetate film is stretched.

[0024] 8. The method for producing an optical compensating film asdescribed in any of above 1 to 7, wherein the water content of thecellulose acetate film just after having been stretched is 2.0 to 20.0%by weight.

[0025] 9. The method for producing an optical compensating film asdescribed in any of above 1 to 8, wherein, when L indicates the distancebetween the fixing members for fixing the cellulose acetate film whenstretching and W indicates the width of the cellulose acetate filmmeasured in the direction perpendicular to the fixing member-to-fixingmember direction, the aspect ratio: L/W satisfies the condition:0.1≦L/W≦2.

[0026] 10. The method for producing an optical compensating film asdescribed in any of above 1 to 9, which comprises a step of stretchingthe cellulose acetate film between at least two pairs of nip rolls by adifference in the rotation speed between the at least two pairs of niprolls.

[0027] 11. The method for producing an optical compensating film asdescribed in above 10, wherein, when W′ (cm) indicates the width of thecellulose acetate film and L′ (cm) indicates the distance between the atleast two pairs of nip rolls, the aspect ratio: L′/W′ satisfies thecondition: 0.5≦L′/W′≦2.

[0028] 12. The method for producing an optical compensating film asdescribed in any of above 1 to 11, wherein the film is stretched inwater.

[0029] 13. The method for producing an optical compensating film asdescribed in any of above 1 to 11, wherein the film is stretched in air.

[0030] 14. The method for producing an optical compensating film asdescribed in any of above 1 to 11, wherein the film is stretched inwater vapor having a relative humidity of from 60% to 100%.

[0031] 15. The method for producing an optical compensating film asdescribed in any of above 1 to 14, wherein the film is stretched at atemperature of 50° C. to 150° C.

[0032] 16. The method for producing an optical compensating film asdescribed in any of above 1 to 15, wherein the film is stretched with adraw ratio of from 1.1 times to 2.0 times.

[0033] 17. The method for producing an optical compensating film asdescribed in any of above 1 to 16, wherein the stretching time is 1second to 30 seconds.

[0034] 18. The method for producing an optical compensating film asdescribed in any of above 1 to 17, wherein the optical compensating filmsatisfies the condition: 1≦(nx−nz)/(nx−ny)≦3, in which nx indicates therefractive index along the slow axis in plain of the opticalcompensating film, ny indicates the refractive index perpendicular tothe slow axis in plane of the optical compensating film, and nzindicates the refractive index of the film in the direction of thethickness thereof.

[0035] 19. The method for producing an optical compensating film asdescribed in any of above 1 to 18, wherein the optical compensating filmhas a haze value of 0 to 2%.

[0036] 20. The method for producing an optical compensating film asdescribed in any of above 1 to 19, wherein the cellulose acetate filmcontains an aromatic compound having at least two aromatic rings in anamount of from 0.01 to 20 parts by weight, based on 100 parts by weightof the film.

[0037] 21. An optical compensating film produced according to the methodfor producing an optical compensating film as described in any of above1 to 20. 22. A polarizing plate, which is a laminate including:

[0038] the optical compensating film produced according to the methodfor producing an optical compensating film as described in any of above1 to 20; and

[0039] at least one of a polarizing film and a polarizing plate.

[0040] 23. An image display comprising at least one of:

[0041] the optical compensating film produced according to the methodfor producing an optical compensating film as described in any of above1 to 20; and

[0042] the polarizing plate as described in above 22.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1 is a schematic view showing a stretching step in which thefilm to be stretched is dipped in water to absorb water and thenstretched in water vapor.

[0044]FIG. 2 is a schematic view showing a stretching step in which thefilm to be stretched is exposed to water vapor to absorb water and thenstretched in water vapor.

[0045]FIG. 3 is a schematic view showing a stretching step in which thefilm to be stretched is dipped in water to absorb water and thenstretched in water.

[0046]FIG. 4 is a schematic view showing a stretching step in which thefilm to be stretched is exposed to water vapor to absorb water and thenstretched in water.

[0047]FIG. 5 is a schematic view showing a stretching step in which thefilm to be stretched is exposed to water vapor to absorb water and thenstretched in water vapor.

[0048]FIG. 6 is a schematic view showing a stretching step in which thefilm to be stretched is exposed to water vapor to absorb water and thenstretched in water.

[0049]FIG. 7 is a schematic plan view showing an obliquely stretchingdevice that is used in Example 6.

[0050]FIG. 8 is a graphic view showing the constitution of thereflection liquid crystal display of the invention.

[0051]FIG. 9 is a cross-sectional view showing the constitution of theVA-mode liquid crystal display of Example 9.

BEST MODES OF CARRYING OUT THE INVENTION

[0052] We, the present inventors have found that, when a celluloseacetate film having an acetyl value (a degree of acetylation) of from57.0% to 62.5% is made to positively absorb water and then stretched,its NZ factor can be controlled. On the basis of this finding, theinventors have attained the optical compensating film of the inventionthat has good optical properties. The invention is described in moredetail hereinunder.

[0053] [Acetate Film]

[0054] For the cellulose acetate film of the invention, preferably usedis cellulose acetate having a degree of acetylation of from 57.0% to62.5%, more preferably from 58.0% to 62.0%.

[0055] The acetyl value (degree of acetylation) is meant to indicate theamount of acetic acid bonded to the cellulose unit by weight. The acetylvalue may be measured and computed according to ASTM D-817-91 (testmethod of cellulose acetate).

[0056] The viscosity-average degree of polymerization (DP) of thecellulose acetate is preferably at least 250, more preferably at least290.

[0057] The cellulose acetate for use in the invention preferably has anarrow molecular weight distribution of Mw/Mn (Mw is a weight-averagemolecular weight, and Mn is a number-average molecular weight) measuredthrough gel permeation chromatography. Concretely, the Mw/Mn value ofthe cellulose acetate is preferably from 1.0 to 1.7, more preferablyfrom 1.3 to 1.65, and most preferably from 1.4 to 1.6.

[0058] Also preferably, the cellulose acetate film for use herein has alight transmittance of at least 80%.

[0059] [Water Content and Water Absorption]

[0060] The cellulose acetate film has a water content of 1.8% by weightat room temperature. In general, the cellulose acetate film (originalfilm) is heated up to around its glass transition point (Tg) so as to bestretchable, and then it is stretched. When the film is heated up toaround its glass transition point, for example, up to 130° C., its watercontent further reduces and it will be 0.4% by weight. The invention ischaracterized in that the cellulose acetate film (original film) in thatcondition is made to absorb water before it is stretched, and the filmto be stretched is made to have a water content of from 2.0% by weightto 20.0% by weight, but preferably from 2.5% by weight to 18.0% byweight, more preferably from 3.0% by weight to 16.0% by weight.

[0061] The water content of the film is the water fraction (% by weight)contained in the film. Concretely, it is indicated by the following:

Water content (% by weight)=0.1×(W/F)

[0062] wherein W represents the amount of water (μg) in the film samplemeasured, which is indicated by the moisture meter used for themeasurement; and F represents the amount of the film sample (mg)measured.

[0063] Having the controlled water content of from 2.0% by weight to20.0% by weight, the cellulose acetate film to be stretched may have alowered glass transition point (Tg). For example, its Tg may be loweredfrom 130° C. (when its water content is 0.4% by weight) to 75° C. (whenits water content is 5.5% by weight). Accordingly, the film can beuniformly stretched at a temperature lower than the ordinary stretchingtemperature (130° C.) thereof.

[0064] Tg of the cellulose acetate film having a water content of 5.5%by weight is measured as follows: The film is dipped in water in aclosed silver pan (70 μl), and its Tg is measured with a varyingtemperature-dependent DSC (TA Instrument's DSC2910).

[0065] In the invention, the cellulose acetate film (original film) tobe stretched is made to absorb water before it is stretched, whereby itswater content can be controlled to fall within the defined range asabove.

[0066] For making it absorb water, the cellulose acetate film to bestretched is dipped in water (water bath method) or exposed to watervapor (water vapor method), or the two methods may be combined.

[0067] When the film is dipped in water, the water temperaturepreferably falls between 60° C. and 100° C., more preferably between 70°C. and 100° C., even more preferably between 75° C. and 100° C.Concretely, the cellulose acetate film to be processed is passed througha water tank filled with water having a temperature that falls withinthe defined range, while conveyed by rolls set in the water tank inwhich it takes from 0.1 to 20 minutes, preferably from 0.2 to 10minutes, more preferably from 0.5 to 5 minutes between the rolls. Thuspassed through the water tank, the film absorbs water.

[0068] For exposure to water vapor, the film may be exposed to watervapor preferably having a temperature of from 60° C. to 150° C., morepreferably from 70° C. to 140° C., even more preferably from 75° C. to130° C., and having a relative humidity of from 70% to 100%, morepreferably from 80% to 100%, even more preferably from 85% to 100%, fora period of from 0.1 to 20 minutes, more preferably from 0.2 to 10minutes, even more preferably from 0.5 to 5 minutes. Thus exposed towater vapor, the film absorbs water. For example, rolls are set in aroom filled with such water vapor, and the cellulose acetate film to beprocessed is conveyed by the rolls in the room to absorb water.

[0069] Water in which the film is dipped or water for water vapor towhich the film is exposed may be any and every one that is substantiallywater. The one that is substantially water is meant to indicate asubstance of which the water content is substantially at least 60% byweight, and it may contain any of organic solvents, plasticizers,surfactants and others except water. The organic solvent that may be inwater for use in the invention is preferably a water-soluble organicsolvent having from 1 to 10 carbon atoms. Preferably, however, wateraccounts for at least 90% by weight of the water mixture for use herein,more preferably at least 95% by weight. Most preferably, water for useherein is pure water.

[0070] The water bath method and the water vapor method may be combinedor may be carried out separately. Especially preferably, the water vapormethod is employed singly.

[0071] Before the cellulose acetate film thus processed to absorb wateris stretched, it is desirable that no water film is substantially formedon its surface. A water film is readily formed on the surface of thecellulose acetate film processed in the manner as above to absorb water,but if it is kept still remaining on the surface of the celluloseacetate film being stretched, the cellulose acetate film will slip onfilm-fixing members such as nip rolls while it is stretched betweenthem. If so, the film could not be stretched with a desired draw ratioand, in addition, it will be readily scratched.

[0072] The condition that “no water film is substantially formed on thesurface of the cellulose acetate film being stretched” in the inventionis meant as follows: Filter paper is pressed against the celluloseacetate film to be stretched, and the area of the filter paper havingabsorbed water from the film is measured. The area thus measured is atmost 30% of the overall area of the filter paper.

[0073] For removing the water film from the wetted cellulose acetatefilm, one preferred method comprises applying a jet of air onto thesurface of the wetted cellulose acetate film through an air knife afterprocessing of absorbing water to thereby blow off water from the surfaceof the film. In this method, if the vapor to be jetted out of the airknife is dry air, the water inside the film will easily evaporate away.Therefore, it is desirable that air having a relative humidity of from70% to 100% is jetted out onto the surface of the wetted celluloseacetate film. As the case may be, water on the surface of the film maybe scraped away with a rubber blade or the like, or the film may becontacted with a roll covered with a water-absorbing cloth to therebyremove water from its surface. These methods may be effected singly ormay be combined. Of those, especially preferred is the method of usingan air knife for water removal from the film surface.

[0074] Preferably, the water removal from the film surface is carriedout in a casing in which the atmosphere has a relative humidity of from70% to 100%. Also preferably, the temperature in the casing iscontrolled to fall between 60° C. and 150° C.

[0075] [Stretching Method]

[0076] The atmosphere in which the film is stretched may be any of air,water vapor or water.

[0077] Stretching in air means that the film is stretched in air ofwhich the temperature is specifically controlled but the humidity isnot. Preferably, the stretching temperature falls between 50° C. and150° C., more preferably between 60° C. and 130° C., even morepreferably between 65° C. and 110° C.

[0078] Stretching in water vapor means that the film is exposed to anatmosphere having a constant temperature and a high humidity or to watervapor. Preferably, the stretching temperature falls between 50° C. and150° C., more preferably between 60° C. and 140° C., even morepreferably between 70° C. and 130° C. Also preferably, the relativehumidity in the water vapor atmosphere falls between 60% RH and 100% RH.In that condition, the water content of cellulose acetate to constitutethe film being stretched is kept between 2.0% by weight and 20.0% byweight. If the water content of the film being stretched is lower than2.0% by weight, the elongation at break thereof is low and the film isreadily broken, and, as a result, the retardation value Re550 of thestretched film measured at a wavelength of 550 nm could not reach λ/4.

[0079] Stretching in water means that the film is stretched while dippedin water in a water tank. Preferably, the temperature of the water fallsbetween 50° C. and 100° C., more preferably between 60° C. and 98° C.,even more preferably between 65° C. and 95° C. Also preferably, thedipping time falls between 0.5 seconds and 10 minutes, more preferablybetween 1 second and 8 minutes, even more preferably between 1 secondand 7 minutes.

[0080] In stretching the film, the aspect ratio L/W preferably fallsbetween 0.05 and 4, more preferably between 0.1 and 3, even morepreferably between 0.1 and 2, in which L indicates the distance betweenthe fixing members by which the film to be stretched is fixed and Windicates the width of the film measured in the direction perpendicularto the fixing member-to-fixing member distance.

[0081] Preferably, the water content of the film just after having beenstretched is kept still falling between 2.0% by weight and 20.0% byweight, since the film in that condition can be uniformly stretched.More preferably, it is kept falling between 2.1% by weight and 18.0% byweight, even more preferably between 2.2% by weight and 16.0% by weight.The water content of the non-stretched film just before the stretchingzone in which it is to be stretched is controlled to fall between 2.0%by weight and 20.0% by weight. Therefore, if the water content of thefilm just after having been stretched is lower than 2.0% by weight, theelongation at break of the stretched film will be low and the frontretardation of the film having a desired thickness could not reach theregion of λ/4.

[0082] The water content of the film just after having been stretched ismeant to indicate the water content of the film just after the step ofstretching the film.

[0083] If desired, water having adhered to the stretched film mayberemoved before the film is wound up. For this, employable is any knownmethod of using an air knife, a blade or the like.

[0084] The film may be stretched in any direction of machine(longitudinal) or transverse (width) direction. As the case may be, thefilm may be stretched in both the machine direction and the transversedirection. The machine direction means the direction in which the filmruns through the stretching apparatus; and the transverse directionmeans the direction that is perpendicular to the machine direction.Especially preferably, the film is monoaxially stretched in any of themachine or transverse direction. More preferably, it is monoaxiallystretched in the machine direction.

[0085] Stretching the film may be effected in any known manner of, forexample, zone stretching, roll stretching or tenter stretching. Ifdesired, the film may be stretched between clips that clip it. In themethod of using clips for stretching the film therebetween, the two endsof the rectangular film are clipped by fixing members such as clips sothat the film does not slip, and the thus-fixed film is stretched. Alsopreferred is the method of stretching the film between rolls, in whichthe film may be stretched in one stage or in multiple stages. In this,the rolls may be disposed in parallel to the film or may cross the film.The rolls are not specifically defined, for which, however, preferredare nip rolls, jacket rolls and expander rolls. More preferred are niprolls that have the advantage of stretching stability.

[0086] Preferably, the draw ratio of the film being stretched falls 1.1times and 2.0 times, more preferably between 1.15 times and 1.9 times,even more preferably between 1.2 times and 1.8 times. The film may bestretched in one stage or in multiple stages. In case where the film isstretched in multiple stages, the product of the draw ratios in eachstage shall fall within the defined range.

[0087] The stretching speed may fall between 10%/min and 1000%/min, butmore preferably between 20%/min and 800%/min, even more preferablybetween 30%/min and 700%/min.

[0088] Preferably, the stretching time falls between 1 and 30 seconds,more preferably between 2 and 25 seconds, even more preferably between 3and 20 seconds.

[0089] Preferably, the thickness of the non-stretched film (film beforestretch) falls between 40 μm and 300 μm, more preferably between 45 μmand 280 μm, even more preferably between 50 μm and 250 μm. Alsopreferably the thickness of the stretched film (film after stretch)falls between 40 μm and 250 μm, more preferably between 50 μm and 230μm, even more preferably between 60 μm and 200 μm.

[0090] Preferably, the width of the non-stretched film falls between 5cm and 3 m, more preferably between 8 cm and 2.5 m, even more preferablybetween 10 cm and 2 m.

[0091] The stretched film is preferably dried. The drying temperaturepreferably falls between 40° C. and 150° C., more preferably between 50°C. and 130° C., even more preferably between 60° C. and 120° C. Thedrying time preferably fall between 10 seconds and 20 minutes, morepreferably between 20 seconds and 10 minutes, even more preferablybetween 30 seconds and 7 minutes.

[0092] It is desirable that the stretched film is dried while it isconveyed to the next stage. Preferably, the tension under which the filmis conveyed falls between 1 kg/m and 50 kg/m, more preferably between 3kg/m and 30 kg/m, even more preferably between 5 kg/m and 20 kg/m.

[0093] [Stretching Method with Nip Rolls]

[0094] The method of stretching the film with nip rolls is described indetail hereinunder.

[0095] At least two pairs, more preferably from 2 pairs to 8 pairs, evenmore preferably from 2 pairs to 6 pairs of nip rolls are used forstretching the film.

[0096] The method of using two pairs of nip rolls is for one-stagestretching; and the method of using three or more pairs of nip rolls isfor multi-stage stretching. A nip pressure is applied to the paired niprolls, and the cellulose acetate film to be stretched is passed betweenthe thus-pressured paired nip rolls while the rotation speed of one pairof roll is made different from that of the other. Thus having beenpassed through the paired nip rolls in that condition, the film isstretched. Concretely, the rotation speed of the nip roll on the outletside (on the downstream side) in the film-traveling direction is madehigher than that of the other nip roll on the inlet side (on theupstream side), and the film running through the nip rolls in thatcondition is stretched and drawn.

[0097] Two nip rolls are paired for stretching the film therebetween,and it is desirable that one or both of them is/are covered with rubber.In the invention, the water content of the film to be stretched is highand the film often slips while it is stretched. Therefore, rubber-coatedrolls are preferred for stretching the film. The rubber material may beany of natural rubber or synthetic rubber (e.g., neoprene rubber,styrene-butadiene rubber, silicone rubber, urethane rubber, butylrubber, nitrile rubber, chloroprene rubber). Preferably, the thicknessof the rubber coating falls between 1 mm and 50 mm, more preferablybetween 2 mm and 40 mm, even more preferably between 3 mm and 30 mm.

[0098] Also preferably, the diameter of each nip roll falls between 5 cmand 100 cm, more preferably between 10 cm and 50 cm, even morepreferably between 15 cm and 40 cm.

[0099] Preferably, the nip rolls for use herein are hollow rolls ofwhich the temperature can be controlled in their hollow inside.

[0100] Regarding the roll-to-roll distance, it is desirable that theaspect ratio L′/W′ satisfies 0.5≦L′/W′≦2, more preferably 0.7≦L′/W′≦1.8,even more preferably 0.9≦L′/W′≦1.6, in which W′ (cm) indicates the widthof the cellulose acetate film and L′ (cm) indicates the distance betweenthe nip rolls. In case where three or more pairs of nip rolls are used,the ratios L′/W′ of every pair of rolls shall be averaged. In general,the aspect ratio of the nip rolls for film stretching is larger than 2.In the invention, it is a matter of importance that the aspect ratio ofthe nip rolls to be used is kept small while the water content of thefilm to be stretched between them is specifically controlled as definedherein, for optimizing the NZ factor of the stretched film.

[0101] The nip pressure to be applied to the nip rolls preferably fallsbetween 0.5 t/m width and 20 t/m width, more preferably between 1 t/mwidth and 10 t/m width, even more preferably between 2 t/m width and 7t/m width.

[0102] In case where the film is stretched between such nip rolls, thestretching temperature preferably falls between 50° C. and 150° C., morepreferably between 60° C. and 140° C., even more preferably between 70°C. and 130° C. In general, the temperature for film stretching isunified both in the transverse direction and in the machine direction.In the invention, however, it is desirable that the film-stretchingtemperature is not unified in at lease one direction. Preferably, thetemperature difference in stretching the film in the invention fallsbetween 1° C. and 20° C., more preferably between 2° C. and 17° C., evenmore preferably between 2° C. and 15° C.

[0103] The film having a specific water content as in the invention hasa lowered glass transition point (Tg), and it can be stretched evenunder low tension. However, the film is often necked in while stretched,and it will be unevenly stretched. To solve the problem, a temperatureprofile of the film being stretched is effective, which is describedbelow.

[0104] (i) Temperature Profile in Machine Direction:

[0105] In film stretching with nip rolls, stress will often concentratein the upstream nip roll outlet (this is the stretching start point),and the film locally receives too much stress in that site, and, as aresult, the film could not often be stretched uniformly. Specifically,for uniformly stretching the film in the entire region in which the filmis stretched, it is desirable that the temperature at the siteimmediately after the upstream nip roll is made lower than the meantemperature in the stretching zone (that is, the temperature in thecenter of the stretching zone in the machine direction) by thetemperature difference mentioned above. The temperature profile instretching the film may be attained, for example, as follows: Atemperature-controllable roll is used for the upstream nip roll and itstemperature is lowered; or a split heat source (e.g., radiation heatsource such as IR heater, or heat jet with multiple jet mouths) isdisposed along the film in its machine direction.

[0106] (ii) Temperature Profile in Transverse Direction:

[0107] The film having the aspect ratio mentioned above is oftenunevenly stretched in the transverse direction thereof. Specifically,both edges of the film are more stretched than the center part thereof.To solve the problem, therefore, it is desirable that the temperature ofboth edges of the film being stretched is kept higher than that of thecenter part thereof in the transverse direction by the temperaturedifference mentioned above. The temperature profile in stretching thefilm may be attained, for example, by disposing a split heat source(e.g., radiation heat source such as IR heater, or heat jet withmultiple jet mouths) around the film in its transverse direction.

[0108] Preferably, the film is stretched between the nip rolls under thecondition as above, for a period of time falling between 1 and 30seconds, more preferably between 2 and 25 seconds, even more preferablybetween 3 and 20 seconds.

[0109] One embodiment of film stretching with nip rolls is describedhereinabove.

[0110] Other embodiments of film stretching in the invention aredescribed below, which may apply not only to nip rolls but also anyothers.

[0111] [Embodiments of Outline Constitution of Stretching Method]

[0112]FIG. 1 to FIG. 6 show the outline constitution of some embodimentsof the stretching method employable in the invention. (In the followingdescription, the parenthesized numerals correspond to the numerals inthe drawings.) Of those, the constitution of FIG. 1 and FIG. 2 ispreferred; and the constitution of FIG. 2 is more preferred.

[0113] In FIG. 1, the film to be stretched is dipped in water to absorbwater and then stretched in water vapor. As illustrated, the film fedfrom a feed roll (1) is conveyed through a water tank (2), in which itabsorbs water to have a water content as specifically defined herein. Asso mentioned hereinabove, it is desirable that the water in the tank isheated. Having passed through the water tank, the film is then led intoa stretching zone, in which the water film on the film surface is firstremoved by air knives (3), and then the film is stretched between twopairs of nip rolls (4).

[0114] Concretely, the rotation speed of the nip rolls on the winding-upside (on the outlet side) is kept higher than that of the nip rolls onthe feeding-out side (on the inlet side), whereby the film is stretchedand drawn between the nip rolls. In this stage, the stretching zone hassteam jet mouths (5), via which steam is jetted out thereinto and thehumidity in the stretching zone is kept within the range as above. Thestretching zone may have multiple steam jet mouths (5) set therein so asto further stabilize the humidity therein. As the case may be, a heater(not shown) may be disposed inside the stretching zone so as to controlthe temperature therein to a predetermined one. After thus stretched,the film is led through a drying zone (6) and then wound up around awind-up roll (7).

[0115] In FIG. 2 and FIG. 5, the film to be stretched is exposed towater vapor to absorb water and then stretched in water vapor. Asillustrated, the film fed out from the roll is exposed to water vaporthat jets out toward it through jet mouths (9), and it absorbs water.The others are the same as those in FIG. 1.

[0116] In FIG. 3, the film to be stretched is dipped in water to absorbwater and then stretched in water. Like in FIG. 1, the film is dipped inwater to absorb water, and then stretched between the nip rolls set in awater tank (8). Preferably, the water in the water tank is heated, as somentioned hereinabove. After thus stretched, the film is dried and woundup in the same manner as in FIG. 1.

[0117] In FIG. 4 and FIG. 6, the film to be stretched is exposed towater vapor to absorb water and then stretched in water. Like in FIG. 2,the film is processed to absorb water, and then this is stretched in thesame manner as in FIG. 3. After thus stretched, the film is dried andwound up in the same manner as in FIG. 1.

[0118] [Film Retardation]

[0119] The film retardation value (Re) is computed according to thefollowing equation:

Retardation Value(Re)=(nx−ny)×d

[0120] wherein nx indicates the refractive index along the slow axis inplain of the optical compensating film (the maximum refractive index inplain of the optical compensating film); ny indicates the refractiveindex perpendicular to the slow axis in plane of the opticalcompensating film, and d indicates the thickness (nm) of the opticalcompensating film.

[0121] Preferably, the retardation measured at a wavelength of 550 nm,Re550 of the optical compensating film of the invention falls between 20nm and 2000 nm, more preferably between 40 nm and 500 nm, even morepreferably between 80 nm and 300 nm.

[0122] Also preferably, the distribution of the retardation valuemeasured at a wavelength of 550 nm, Re550 of the optical compensatingfilm is at most 10% in both the transverse direction and the machinedirection of the film.

[0123] In particular, in case where the optical compensating film of theinvention is used for a λ/4 plate, it is desirable that the retardationvalue measured at a wavelength of 450 nm (Re450) of the film fallsbetween 60 and 135 nm, the retardation value measured at a wavelength of590 nm (Re590) thereof falls between 100 and 170 nm, and the filmsatisfies Re590−Re450≧2 nm. More preferably, the film satisfiesRe590−Re450≧5 nm, most preferably Re590−Re450>10 nm.

[0124] In case where the optical compensating film of the invention isused for a λ/2 plate, it is desirable that the retardation valuemeasured at a wavelength of 450 nm (Re450) of the film falls between 120and 270 nm, the retardation value measured at a wavelength of 590 nm(Re590) thereof falls between 200 and 340 nm, and the film satisfiesRe590−Re450>4 nm. More preferably, the film satisfies Re590−Re450≧10 nm,most preferably Re590−Re450≧20 nm.

[0125] In any case of using the film for a λ/4 plate or λ/2 plate, it isdesirable that the retardation value measured at a wavelength of 450 nm,550 nm or 650 nm: Re450, Re550 and Re650 of the film satisfy thefollowing:

0.5<Re450/Re550<0.98,

1.01<Re650/Re550<1.35.

[0126] More preferably,

0.6<Re450/Re550<0.95,

1.05<Re650/Re550<1.3.

[0127] Even more preferably,

0.7<Re450/Re550<0.9,

1.1<Re650/Re550<1.25.

[0128] [NZ Factor]

[0129] Preferably, the cellulose acetate film used singly in theinvention satisfies the following equation:

1≦(nx−nz)/(nx−ny)≦3

[0130] wherein nx indicates the refractive index along the slow axis inplain of the optical compensating film, ny indicates the refractiveindex perpendicular to the slow axis in plane of the opticalcompensating film, and nz indicates the refractive index of the film inthe direction of the thickness thereof.

[0131] In the invention, the NZ factor is a value indicated by(nx−nz)/(nx−ny). Preferably, the NZ factor falls between 1.1 and 2.8,more preferably between 1.2 and 2.7, even more preferably between 1.5and 2.5. Satisfying the condition, the method of the invention producesbetter results.

[0132] [Haze]

[0133] The haze of the optical compensating film of the invention iscomputed according to the equation mentioned below, and it is preferablyat most 2.0%, more preferably at most 1.0%, most preferably at most0.6%.

Haze(HZ)=[diffusion(D)/total transmittance(T)]×100(%)

[0134] wherein the diffusion (D) indicates the intensity of the lightdiffused by the film, and this is measured with a haze meter; and thetotal transmittance (T) indicates the mean transmittance of visiblelight of from 400 to 700 nm, through the film.

[0135] The optical compensating film of a cellulose acetate film havingthe above-mentioned optical properties may be produced, using thematerials mentioned below.

[0136] [Retardation-Controlling Agent]

[0137] For controlling the retardation value of the film at differentwavelengths, it is desirable that a retardation-controlling agent isadded to cellulose acetate for the film.

[0138] Preferably, the amount of the retardation-controlling agent to beadded to cellulose acetate falls between 0.01 and 30 parts by weightrelative to 100 parts of cellulose acetate, more preferably between 0.05and 25 parts by weight, even more preferably between 0.1 and 20 parts byweight. If desired, two or more different types ofretardation-controlling agents may combined and used herein.

[0139] Preferably, the retardation-controlling agent for use herein hasa maximum absorption wavelength in a wavelength range of from 210 to 360nm. Also preferably, the retardation-controlling agent does notsubstantially absorb visible light.

[0140] For the retardation-controlling agent, preferred are compoundshaving at least two “aromatic rings”. The “aromatic ring” referred toherein includes aromatic hydrocarbon rings and aromatic hetero-rings.

[0141] Especially preferably, the aromatic hydrocarbon ring to be in thecompound for the agent is a 6-membered ring (i.e., benzene ring).

[0142] The aromatic hetero-rings are generally unsaturated hetero-rings,for which preferred are 5-membered, 6-membered and 7-membered rings.More preferred are 5-membered and 6-membered rings. The aromatichetero-rings generally have a largest number of double bonds. For theheteroatom in these, preferred are nitrogen, oxygen and sulfur atoms;and more preferred is a nitrogen atom. Examples of the aromatichetero-rings include furan, thiophene, pyrrole, oxazole, isoxazole,thiazole, isothiazole, imidazole, pyrazole, furazane, triazole, pyran,pyridine, pyridazine, pyrimidine, pyrazine and 1,3,5-triazine rings.

[0143] For the aromatic rings, for example, preferred are benzene,furan, thiophene, pyrrole, oxazole, thiazole, imidazole, triazole,pyridine, pyrimidine, pyrazine and 1,3,5-triazine rings.

[0144] Preferably, the number of such aromatic rings to be in thecompound for the retardation-controlling agent for use herein is from 2to 20, more preferably from 2 to 12, most preferably from 2 to 6.

[0145] The retardation-controlling agent of the type may be any of (α)tabular compounds or (β) rod compounds mentioned below. One or morethese compounds may be used either singly or as combined for the agent.

[0146] (α) Tabular Compounds:

[0147] The tabular compounds each contain at least two pairs of aromaticrings, in which the bonding mode of the two aromatic rings is groupedinto (a) a case of forming a condensed ring, (b) a case of directlybonding to each other via a single bond, and (c) a case of bonding toeach other via a linking group (however, the aromatic rings could notform a spiro bond). In the compounds, the bonding mode of the aromaticrings may be any of (a) to (c).

[0148] Examples of the case (a) condensed ring (composed of at least twoaromatic rings) include indene, naphthalene, azulene, fluorene,phenanthrene, anthracene, acenaphthylene, biphenylene, naphthacene,pyrene, indole, isoindole, benzofuran, benzothiophene, indolidine,benzoxazole, benzothiazole, benzimidazole, benzotriazole, purine,indazole, chromene, quinoline, isoquinoline, quinolidine, quinazoline,cinnoline, quinoxaline, phthalazine, pteridine, carbazole, acridine,phenanthridine, xanthene, phenazine, phenothiazine, phenoxthine,phenoxazine and thianthrene rings. Of those, preferred are naphthalene,azulene, indole, benzoxazole, benzothiazole, benzimidazole,benzotriazole and quinoline rings.

[0149] The single bond in (b) is preferably a carbon-carbon bond thatbonds two aromatic rings. If desired, however, two or more single bondsmay bond two aromatic rings to thereby form an aliphatic ring or anon-aromatic hetero-ring between the thus-bonded two rings.

[0150] Also preferably, the linking group in (c) bonds to the carbonatoms of two aromatic rings. Preferred examples of the linking group arean alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—,—NH—, —S—, and their combinations. Some examples of combined linkinggroups are mentioned below, in which the right and left configurationsof the linking groups may be reversed.

[0151] c1: —CO—O—

[0152] c2: —CO—NH—

[0153] c3: -alkylene-O—

[0154] c4: —NH—CO—NH—

[0155] c5: —NH—CO—O—

[0156] c6: —O—CO—O—

[0157] c7: —O-alkylene-O—

[0158] c8: —CO-alkenylene-

[0159] c9: —CO-alkenylene-NH—

[0160] c10: —CO-alkenylene-O—

[0161] c11: -alkylene-CO—O-alkylene-O—CO-alkylene-

[0162] c12: —O-alkylene-CO—O-alkylene-O—CO-alkylene-O—

[0163] c13: —O—CO-alkylene-CO—O—

[0164] c14: —NH—CO-alkenylene-

[0165] c15: —O—CO-alkenylene-

[0166] The aromatic rings and the linking groups may have substituents.

[0167] Examples of the substituents include a halogen atom (F, Cl, Br,I), a hydroxyl group, a carboxyl group, a cyano group, an amino group, anitro group, a sulfo group, a carbamoyl group, a sulfamoyl group, anureido group, an alkyl group, an alkenyl group, an alkynyl group, analiphatic acyl group, an aliphatic acyloxy group, an alkoxy group, analkoxycarbonyl group, an alkoxycarbonylamino group, analkylthio group,an alkylsulfonyl group, an aliphatic amido group, an aliphaticsulfonamido group, an aliphatic substituted amino group, an aliphaticsubstituted carbamoyl group, an aliphatic substituted sulfamoyl group,an aliphatic substituted ureido group, and a non-aromatic heterocyclicgroup.

[0168] Preferably, the alkyl group has from 1 to 8 carbon atoms. For it,an acyclic alkyl group is preferred to a cyclic alkyl group, and alinear alkyl group is especially preferred. The alkyl group may befurther substituted (for example, with any of a hydroxyl group, acarboxyl group, an alkoxy group and an alkyl-substituted amino group).Examples of the alkyl group (including substituted alkyl groups) aremethyl, ethyl, n-butyl, n-hexyl, 2-hydroxyethyl, 4-carboxybutyl,2-methoxyethyl and 2-diethylaminoethyl groups.

[0169] Preferably, the alkenyl group has from 2 to 8 carbon atoms. Forit, an acyclic alkenyl group is preferred to a cyclic alkenyl group, anda linear alkenyl group is especially preferred. The alkenyl group may befurther substituted. Examples of the alkenyl group include vinyl, allyland 1-hexenyl groups.

[0170] Preferably, the alkynyl group has from 2 to 8 carbon atoms. Forit, an acyclic alkynyl group is preferred to a cyclic alkynyl group, anda linear alkynyl group is especially preferred. The alkynyl group may befurther substituted. Examples of the alkynyl group include ethynyl,1-butynyl and 1-hexynyl groups.

[0171] Preferably, the aliphatic acyl group has from 1 to 10 carbonatoms. Examples of the aliphatic acyl group include acetyl, propanoyland butanoyl groups.

[0172] Preferably, the aliphatic acyloxy group has from 1 to 10 carbonatoms. One example of the aliphatic acyloxy group is an acetoxy group.

[0173] Preferably, the alkoxy group has from 1 to 8 carbon atoms. Thealkoxy group may be further substituted (for example, with an alkoxygroup). Examples of the alkoxy group (including substituted alkoxygroups) are methoxy, ethoxy, butoxy and methoxyethoxy groups.

[0174] Preferably, the alkoxycarbonyl group has from 2 to 10 carbonatoms. Examples of the alkoxycarbonyl group include methoxycarbonyl andethoxycarbonyl groups.

[0175] Preferably, the alkoxycarbonylamino group has from 2 to 10 carbonatoms. Examples of the alkoxycarbonylamino group includemethoxycarbonylamino and ethoxycarbonylamino groups.

[0176] Preferably, the alkylthio group has from 1 to 12 carbon atoms.Examples of the alkylthio group include methylthio, ethylthio andoctylthio groups.

[0177] Preferably, the alkylsulfonyl group has from 1 to 8 carbon atoms.Examples of the alkylsulfonyl group include methanesulfonyl andethanesulfonyl groups.

[0178] Preferably, the aliphatic amido group has from 1 to 10 carbonatoms. One example of the aliphatic amido group is an acetamido group.

[0179] Preferably, the aliphatic sulfonamido group has from 1 to 8carbon atoms. Examples of the aliphatic sulfonamido group includemethanesulfonamido, butanesulfonamido and n-octanesulfonamido groups.

[0180] Preferably, the aliphatic substituted amino group has from 1 to10 carbon atoms. Examples of the aliphatic substituted amino groupinclude dimethylamino, diethylamino and 2-carboxyethylamino group.

[0181] Preferably, the aliphatic substituted carbamoyl group has from 2to 10 carbon atoms. Examples of the aliphatic substituted carbamoylgroup include methylcarbamoyl and diethylcarbamoyl groups.

[0182] Preferably, the aliphatic substituted sulfamoyl group has from 1to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl groupinclude methylsulfamoyl and diethylsulfamoyl groups.

[0183] Preferably, the aliphatic substituted ureido group has from 2 to10 carbon atoms. One example of the aliphatic substituted ureido groupus a methylureido group.

[0184] Examples of the non-aromatic heterocyclic group includepiperidino and morpholino groups.

[0185] Preferably, the molecular weight of the retardation-controllingagent falls between 300 and 800. Specific examples of such tabularretardation-controlling agents are described, for example, inInternational Patent Laid-Open No. WO 00/65384.

[0186] (β) Rod Compounds:

[0187] In the invention, rod compounds having a maximum absorption in ashort wavelength range shorter than 250 nm are also preferred for theretardation-controlling agent.

[0188] In view of their function as the retardation-controlling agent,the rod compounds for use herein preferably have at least one aromaticring, more preferably at least two aromatic rings each.

[0189] Also preferably, the rod compounds have a linear molecularstructure. The linear molecular structure is meant to indicate that themolecular structure of the rod compound is linear when it is the moststable in point of its thermodynamic aspect. The structure of thecompound that is the most stable in point of its thermodynamic aspectcan be determined through crystal structure analysis or molecularorbital computation. For example, using a molecular orbital computationsoftware (e.g., WinMOPAC2000 from Fujitsu), the compound is analyzedthrough molecular orbital computation, and its molecular structure withwhich the heat of forming the compound is the smallest is determined.The linear molecular structure is meant to indicate that the angle ofthe molecular structure that has been found to be the most stable inpoint of its thermodynamic aspect through the computation as above is atleast 140 degrees.

[0190] For the rod compounds for use herein, preferred are those of thefollowing formula (I):

Ar¹-L¹-Ar²  (I)

[0191] In formula (I), Ar¹ and Ar² each independently represent anaromatic group.

[0192] In the present description, the aromatic group includes an arylgroup (aromatic hydrocarbon group), a substituted aryl group, anaromatic heterocyclic group and a substituted aromatic heterocyclicgroup.

[0193] For it, aryl and substituted aryl groups are preferred toaromatic heterocyclic and substituted aromatic heterocyclic groups. Thehetero-ring in the aromatic heterocyclic group is generally unsaturated.Preferably, the aromatic hetero-ring is a 5-membered, 6-membered or7-membered ring, more preferably a 5-membered or 6-membered ring. Thearomatic hetero-ring generally has a largest number of double bonds. Forthe heteroatom in the ring, preferred is any of nitrogen, oxygen orsulfur atom, and more preferred is nitrogen or sulfur atom. Examples ofthe aromatic hetero-rings include furan, thiophene, pyrrole, oxazole,isoxazole, thiazole, isothiazole, imidazole, pyrazole, furazane,triazole, pyran, pyridine, pyridazine, pyrimidine, pyrazine and1,3,5-triazine rings.

[0194] Preferred examples of the aromatic ring for the aromatic groupare benzene, furan, thiophene, pyrrole, oxazole, thiazole, imidazole,triazole, pyridine, pyrimidine and pyrazine rings; and more preferredfor it is a benzene ring.

[0195] Examples of the substituents for the substituted aryl group andthe substituted aromatic heterocyclic group include a halogen atom (F,Cl, Br, I), a hydroxyl group, a carboxyl group, a cyano group, an aminogroup, an alkylamino group (e.g., methylamino, ethylamino, butylamino,dimethylamino), a nitro group, a sulfo group, a carbamoyl group, analkylcarbamoyl group (e.g., N-methylcarbamoyl, N-ethylcarbamoyl,N,N-dimethylcarbamoyl), a sulfamoyl group, an alkylsulfamoyl group(e.g., N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dimethylsulfamoyl), anureido group, an alkylureido group (e.g., N-methylureido,N,N-dimethylureido, N,N,N′-trimethylureido), an alkyl group (e.g.,methyl, ethyl, propyl, butyl, pentyl, heptyl, octyl, isopropyl, s-butyl,t-amyl, cyclohexyl, cyclopentyl), analkenyl group (e.g., vinyl, allyl,hexenyl), an alkynyl group (e.g., ethynyl, butynyl), an acyl group(e.g., formyl, acetyl, butyryl, hexanoyl, lauryl), an acyloxy group(e.g., acetoxy, butyryloxy, hexanoyloxy, lauryloxy), an alkoxy group(e.g., methoxy, ethoxy, propoxy, butoxy, pentyloxy, heptyloxy,octyloxy), an aryloxy group (e.g., phenoxy), an alkoxycarbonyl (e.g.,methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl,pentyloxycarbonyl, heptyloxycarbonyl), an aryloxycarbonyl group (e.g.,phenoxycarbonyl), an alkoxycarbonylamino group (e.g.,butoxycarbonylamino, hexyloxycarbonylamino), an alkylthio group (e.g.,methylthio, ethylthio, propylthio, butylthio, pentylthio, heptylthio,octylthio), an arylthio group (e.g., phenylthio), an alkylsulfonyl group(e.g., methylsulfonyl, ethylsulfonyl, propylsulfonyl, butylsulfonyl,pentylsulfonyl, heptylsulfonyl, octylsulfonyl), an amido group (e.g.,acetamido, butylamido, hexylamido, laurylamido), and a non-aromaticheterocyclic group (e.g., morpholyl, pyrazinyl).

[0196] For the substituents for the substituted aryl group and thesubstituted aromatic heterocyclic group, preferred are a halogen atom, acyano group, a carboxyl group, a hydroxyl group, an amino group, analkyl-substituted amino group, an acyl group, an acyloxy group, an amidogroup, an alkoxycarbonyl group, an alkoxy group, an alkylthio group andan alkyl group.

[0197] The alkyl moiety in the alkylamino group, the alkoxycarbonylgroup, the alkoxy group and the alkylthio group, and also the alkylgroup may be further substituted. Examples of the substituents for thealkyl moiety and the alkyl group include a halogen atom, a hydroxylgroup, a carboxyl group, a cyano group, an amino group, an alkylaminogroup, a nitro group, a sulfo group, a carbamoyl group, analkylcarbamoyl group, a sulfamoyl group, an alkylsulfamoyl group, anureido group, an alkylureido group, an alkenyl group, an alkynyl group,an acyl group, an acyloxy group, an alkoxy group, an aryloxy group, analkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylaminogroup, an alkylthio group, an arylthio group, an alkylsulfonyl group, anamido group and a non-aromatic heterocyclic group. For the substituentsfor the alkyl moiety and the alkyl group, preferred are a halogen atom,a hydroxyl group, an amino group, an alkylamino group, an acyl group, anacyloxy group, an acylamino group, an alkoxycarbonyl group and an alkoxygroup.

[0198] In formula (I), L¹ represents a divalent linking group selectedfrom an alkylene group, an alkenylene group, an alkynylene group, —O—,—CO— and their combinations.

[0199] The alkylene group may have a cyclic structure. The cyclicalkylene group is preferably a cyclohexylene group, more preferably a1,4-cyclohexylene group. For the acyclic alkylene group, a linearalkylene group is preferred to a branched alkylene group.

[0200] Preferably, the alkylene group has from 1 to 20 carbon atoms,more preferably from 1 to 15 carbon atoms, even more preferably from 1to 10 carbon atoms, still more preferably from 1 to 8 carbon atoms, mostpreferably from 1 to 6 carbon atoms.

[0201] Preferably, the alkenylene group and the alkynylene group have anacyclic structure but not a cyclic structure. More preferably, they havea linear structure but not a branched structure.

[0202] Also preferably, the alkenylene group and the alkynylene grouphave from 2 to 10 carbon atoms, more preferably from 2 to 8 carbonatoms, even more preferably from 2 to 6 carbon atoms, still morepreferably from 2 to 4 carbon atoms each. Most preferred is a 2-vinylene(or ethynylene) group.

[0203] Examples of the combined, divalent linking groups are mentionedbelow.

[0204] L-1: —O—CO-alkylene-CO—O—

[0205] L-2: —CO—O-alkylene-O—CO—

[0206] L-3: —O—CO-alkenylene-CO—O—

[0207] L-4: —CO—O-alkenylene-O—CO—

[0208] L-5: —O—CO-alkynylene-CO—O—

[0209] L-6: —CO—O-alkynylene-O—CO—

[0210] In the molecular structure of formula (I), it is desirable thatthe angle at which Ar¹ meets Ar² via L¹ therebetween is at least 140degrees.

[0211] More preferably, the rod compounds for use herein are those ofthe following formula (II):

Ar¹-L²-X-L³-Ar²  (II)

[0212] In formula (II), Ar¹ and Ar² each independently represent anaromatic group. The definition and the examples of the aromatic groupare the same as those mentioned hereinabove for Ar¹ and Ar² in formula(I).

[0213] In formula (II), L² and L³ each independently represent adivalent linking group selected from an alkylene group, —O—, —CO—, andtheir combinations.

[0214] Preferably, the alkenylene group has an acyclic structure but nota cyclic structure. More preferably, it has a linear structure but not abranched structure.

[0215] Also preferably, the alkenylene group has from 1 to 10 carbonatoms, more preferably from 1 to 8 carbon atoms, even more preferablyfrom 1 to 6 carbon atoms, still more preferably from 1 to 4 carbonatoms, most preferably 1 or 2 carbon atoms (methylene or ethylene).

[0216] Especially preferably, L² and L³ eachare-O—CO— or —CO—O—.

[0217] In formula (II), X represents a 1,4-cyclohexylene, vinylene orethynylene group.

[0218] Specific examples of the compounds of formula (I) are mentionedbelow.

[0219] Compounds (1) to (34), (41) and (42) each have two asymmetriccarbon atoms at the 1- and 4-positions of the cyclohexane ring therein.However, since compounds (1), (4) to (34), (41) and (42) have asymmetric meso-type molecular structure, they do not include opticalisomers (with optical activity) but have only geometric isomers (trans-and cis-isomers). 1-trans and 1-cis structures of compound (1) are shownbelow.

[0220] As so mentioned hereinabove, the rod compounds for use hereinpreferably have a linear molecular structure. Accordingly, trans-isomersare preferred to cis-isomers of the compounds.

[0221] Compounds (2) and (3) have both geometric isomers and opticalisomers (totaling four isomers). Of the geometric isomers thereof,trans-isomers are preferred to cis-isomers. However, there is nospecific difference between the optical isomers of the compounds inpoint of their superiority. The optical isomers may be any of D- orL-isomers or even racemates.

[0222] In compounds (43) to (45), the center vinylene bond includestrans-and cis-structures. For the same reason as above, trans-structuresare also preferred to cis-structures of these compounds.

[0223] Two or more different types of such rod compounds of which themaximum absorption wavelength (λmax) is shorter than 250 nm in solutionUV absorptiometry may be combined and used in the invention.

[0224] The rod compounds may be produced with reference to the methodsdescribed in literature. The literature disclosing the methods includes,for example, Mol. Cryst. Liq. Cryst., Vol. 53, p. 229 (1979); ibid.,Vol. 89, p. 93 (1982); ibid., Vol. 145, p. 111 (1987); ibid., Vol. 170,p. 43 (1989); J. Am. Chem. Soc., Vol. 113, p. 1349 (1991); ibid., Vol.118, p. 5346 (1886); ibid., Vol. 92, p. 1582 (1970); J. Org. Chem., Vol.40, p. 420 (1875); Tetrahedron, Vol. 48, No. 16, p. 3437 (1992).

[0225] (Spectrometry of Retardation-Controlling Compounds)

[0226] The UV and visible range (UV-vis) spectrum of the above-mentionedretardation-controlling agent (10-trans) was measured. Concretely, theretardation-controlling agent (10-trans) was dissolved intetrahydrofuran (not containing a stabilizer, BHT (butylatedhydroxytoluene)) to prepare its solution having a concentration of 10⁻⁵mol/dm³. The resulting solution was measured with a spectrophotometer(from Hitachi), and the wavelength at which the solution showed amaximum absorption (λmax) was 220 nm. The absorption coefficient (e) ofthe compound solution was 15000. In the same manner as above, theretardation-controlling agent (29-trans) was analyzed, and thewavelength at which the compound solution showed a maximum absorption(λmax) was 240 nm. The absorption coefficient (ε) of the compoundsolution was 20000. Also in the same manner, the retardation-controllingagent (41-trans) was analyzed, and the wavelength at which the compoundsolution showed a maximum absorption (λmax) was 230 nm. The absorptioncoefficient (ε) of the compound solution was 16000.

[0227] One or more retardation-controlling compounds may be used in theinvention, either singly or as combined.

[0228] [Production of Cellulose Acetate Film]

[0229] The cellulose acetate film for use in the invention is preferablyproduced in a solvent-casting method. In the solvent-casting method, thepolymer material for the film is dissolved in an organic solvent and theresulting solution (dope) is cast to form the intended polymer film.

[0230] One example of the method of producing the cellulose acetate filmof the invention is described concretely, using cellulose acetate.

[0231] The organic solvent is preferably selected from ethers havingfrom 3 to 12 carbon atoms, ketones having from 3 to 12 carbon atoms,esters having from 3 to 12 carbon atoms, and halogenohydrocarbons havingfrom 1 to 6 carbon atoms.

[0232] These ethers, ketones and esters may have a cyclic structure.Compounds having at least two functional groups of ethers, ketones andesters (i.e., —O—, —CO— and —COO—) may also be used for the organicsolvent. The organic solvent for use herein may have any otherfunctional group such as an alcoholic hydroxyl group. The number ofcarbon atoms that constitute the organic solvent having two or morefunctional groups shall fall within the defined range of the compoundshaving any one of the functional groups.

[0233] Examples of the ethers having from 3 to 12 carbon atoms includediisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane,1,3-dioxolane, tetrahydrofuran, anisole and phenetole.

[0234] Examples of the ketones having from 3 to 12 carbon atoms includeacetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone,cyclohexanone and methylcyclohexanone.

[0235] Examples of the esters having from 3 to 12 carbon atoms includeethyl formate, propyl formate, pentyl formate, methyl acetate, ethylacetate and pentyl acetate.

[0236] Examples of the organic solvent having two or more functionalgroups include 2-ethoxyethyl acetate, 2-methoxyethanol and2-butoxyethanol.

[0237] Preferably, the halogenohydrocarbons for the organic solvent have1 or 2 carbon atoms, most preferably one carbon atom. The halogen in thehalogenohydrocarbons is preferably chlorine. Preferably, the degree ofhydrogen substitution with halogen in the halogenohydrocarbons fallsbetween 25 and 75 mol %, more preferably between 30 and 70 mol %, evenmore preferably between 35 and 65 mol %, most preferably between 40 and60 mol %. One typical example of the halogenohydrocarbons is methylenechloride.

[0238] Two or more different organic solvents may be mixed and usedherein.

[0239] A cellulose acetate solution may be prepared in any ordinarymanner. The ordinary manner is meant to indicate that the solution isprepared at a temperature not lower than 0° C. (room temperature or hightemperature). For preparing the solution, employable are any knownmethod and device that are generally used in preparing dopes in anordinary solvent-casting method. In the ordinary method, ahalogenohydrocarbon (especially methylene chloride) is preferably usedfor the organic solvent.

[0240] The amount of cellulose acetate to be dissolved in the organicsolvent is so controlled that the resulting solution has a celluloseacetate content of from 10 to 40% by weight. More preferably, thecellulose acetate content of the solution falls between 10 and 30% byweight. Any optional additive that will be mentioned hereinunder may beadded to the organic solvent (main solvent).

[0241] The intended solution may be prepared by stirring celluloseacetate in the organic solvent at room temperature (0 to 40° C.). Thesolution of high concentration may be stirred under heat and pressure.Concretely, cellulose acetate and the organic solvent are put into apressure vessel and sealed up therein, and these are stirred underpressure while heated at a temperature not lower than the boiling pointat room temperature of the solvent but at which the solvent does notboil. The heating temperature is generally 40° C. or higher, preferablyfalling between 60 and 200° C., more preferably between 80 and 110° C.

[0242] The individual components may be put into the vessel after theyare roughly pre-mixed. Alternatively, they may be put thereinto oneafter another. The vessel must be so constituted that it allows thecontents to be stirred therein. An inert vapor such as nitrogen gas maybe introduced into the vessel to increase the pressure in the vessel.For the pressure increase, the increased vapor pressure of the heatedsolvent may also be utilized. As the case may be, after the vessel issealed up, the components may be forced thereinto under pressure.

[0243] Preferably, the vessel with the components therein is heated byan external heating unit. For it, for example, usable is a jacketheater. Alternatively, a plate heater may be provided outside thevessel, and a liquid is circulated therein so as to entirely heat thevessel.

[0244] Preferably, a stirring blade is disposed inside the vessel, withwhich the contents of the vessel may be stirred. It is desirable thatthe stirring blade is so long as to reach near the inner wall of thevessel. Also preferably, the end edges of the stirring blade areprovided with a scraper that serves to renew the liquid film formed onthe inner wall of the vessel.

[0245] If desired, the vessel may be equipped with some meters such as apressure gauge and a thermometer. In the vessel, the components aredissolved in the solvent. The dope thus prepared is taken out after ithas been cooled in the vessel; or after directly taken out of thevessel, it may be cooled with a heat exchanger or the like.

[0246] The solution may also be prepared in a cooling dissolutionmethod. In the cooling dissolution method, cellulose acetate can bedissolved even in an organic solvent in which it is difficult todissolve in an ordinary dissolving method. For the organic solvent forcellulose acetate, methylene chloride is generally used. However,methylene chloride is not good for global environment protection and forworking environment protection, and it is undesirable to use it. In anorganic solvent system not containing methylene chloride, celluloseacetate is difficult to dissolve in an ordinary dissolving method. Forthat system, the cooling dissolution method is effective. Even for othersolvents in which cellulose acetate can be dissolved in an ordinarydissolving method, the cooling dissolution method is also effective asit rapidly produces a uniform solution.

[0247] In the cooling dissolution method, cellulose acetate is firstgradually added to an organic solvent at room temperature with stirring.

[0248] Preferably, the amount of cellulose acetate to be added is socontrolled that the resulting mixture may contain from 10 to 40% byweight, more preferably from 10 to 30% by weight of cellulose acetate.If desired, any optional additive that will be mentioned hereinunder maybe added to the mixture.

[0249] Next, the mixture is cooled to a temperature falling between−100° C. and −10° C., preferably between −80° C. and −10° C., morepreferably between −50° C. and −20° C., most preferably between −50 and−30° C. Cooling it may be effected, for example, in a dry ice/methanolbath (−75° C.) or in a cooled diethylene glycol solution (from −30 to−20° C.). Thus cooled, the mixture of cellulose acetate and the organicsolvent is solidified.

[0250] Preferably, the cooling rate is at least 4° C./min, morepreferably at least 8° C./min, most preferably at least 12° C./min.Higher cooling rate is better, but the theoretical uppermost limit ofthe cooling rate is 10000° C./sec, the technical uppermost limit thereofis 1000° C./sec, and the practical uppermost limit thereof is 100°C./sec. The cooling rate is obtained by dividing the difference betweenthe temperature at which the cooling is started and the final coolingtemperature by the time taken by the process to reach the final coolingtemperature from the start of cooling.

[0251] Then, the thus-cooled mixture is heated up to a temperaturefalling between 0° C. and 200° C., preferably between 0° C. and 150° C.,more preferably between 0° C. and 120° C., most preferably between 0° C.and 50° C., through which cellulose acetate dissolves in the organicsolvent. Heating the mixture may be effected merely by leaving it atroom temperature, or the mixture may be heated in a hot bath.

[0252] Preferably, the heating rate is at least 4° C./min, morepreferably at least 8° C./min, most preferably at least 12° C./min.Higher heating rate is better, but the theoretical uppermost limit ofthe heating rate is 10000° C./sec, the technical uppermost limit thereofis 1000° C./sec, and the practical uppermost limit thereof is 100°C./sec. The heating rate is obtained by dividing the difference betweenthe temperature at which the heating is started and the final heatingtemperature by the time taken by the process to reach the final heatingtemperature from the start of heating.

[0253] A uniform solution of cellulose acetate can be obtained accordingto the method as above. If cellulose acetate dissolution is stillinsufficient, the operations of cooling and heating may be repeated.Whether the dissolution is sufficient or not can be judged only byvisually observing the external appearance of the solution.

[0254] In the cooling dissolution method, it is preferred to use aclosed vessel so that water from dew formation in cooling the mixturedoes not enter the mixture. In the cooling and heating process, pressureapplication during cooling and pressure reduction during heating resultin the reduction in the period of time taken for dissolution. Forpressure application and pressure reduction, preferred is a pressurevessel.

[0255] It has been confirmed through differential scanning calorimetry(DSC) that the 20 wt. % solution obtained by dissolving celluloseacetate (degree of acetylation: 60.9%, viscosity-average degree ofpolymerization: 299) in methyl acetate in the cooling dissolution methodhas a pseudo phase transition point of around 33° C. at which itundergoes sol-gel change. At a temperature lower than the pseudo phasetransition point, the solution forms a uniform gel. Accordingly, thesolution must be kept at a temperature not lower than the pseudo phasetransition point, preferably at a temperature higher than the pseudophase transition point by about 10° C. However, the pseudo phasetransition point of the solution varies depending upon the degree ofacetylation and the viscosity-average degree of polymerization ofcellulose acetate in the solution, and on the solution concentration andthe organic solvent used.

[0256] A cellulose acetate film is formed from the thus-preparedcellulose acetate solution (dope) in a solvent casting method.

[0257] A film is formed by casting the dope on a drum or a band andevaporating the solvent from it. Preferably, the dope to be cast is socontrolled that its solid content falls between 18 and 35% by weight.The surface of the drum or the band is preferably finished to have amirror surface. The methods of casting and drying the film in thesolvent casting method are disclosed in U.S. Pat. Nos. 2,336,310,2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704,2,739,069,2,739,070; British Patents 640,731, 736,892; JP-B 4554/1970, 5614/1974;JP-A 176834/1985, 203430/1985, 115035/1987.

[0258] It is preferred to cast the dope on a drum or a band having asurface temperature not higher than 10° C. It is also preferred to drythe cast dope by applying thereto wind for at least 2 seconds. Theformed film may be peeled from the drum or the band and may be furtherdried by applying thereto high-temperature wind that gradually variesfrom 100 to 160° C. to thereby evaporate away the remaining solvent.This method is disclosed in JP-B 17844/1993. According to these methods,the time to be taken from casting the solution to peeling off the filmcan be reduced. In this method, it is necessary that the dope should gelat the surface temperature of the drum or the band on which it is cast.

[0259] One or more films may be formed by casting the cellulose acetatesolution (dope) prepared in the above, according to the solvent castingmethod. For this, the dope is cast on a drum or a band, and the solventis evaporated away to form the intended film. Before cast, the dope ispreferably so controlled that its solid content falls between 10 and40%. Also preferably, the surface of the drum or the band ismirror-finished.

[0260] In case where at least two cellulose acetate solutions for atleast two films are cast, the cellulose acetate solutions are cast on asupport through the respective casting mouths that are provided atintervals in the machine direction of the support to thereby laminatethe resulting films on the support. For this, for example, hereinemployable are the methods described in JP-A 158414/1986, 122419/1989,198285/1999. The cellulose acetate solution may be cast through twocasting mouths to form the film. For this, for example, hereinemployable are the methods described in JP-B 27562/1985; JP-A94724/1986, 94725/1986, 104813/1986, 158413/1986, 134933/1994. A partfrom these, the casting method described in JP-A 162617/1981 is alsoemployable herein, in which the flow of a high-viscosity celluloseacetate solution is enveloped in a low-viscosity cellulose acetatesolution and the two, high-viscosity and low-viscosity cellulose acetatesolutions are co-extruded out to form a cellulose acetate film.

[0261] Alternatively, two casting mouths may be used for film formationin such a manner that the film formed on a support through the firstcasting mouth is peeled off and another film is formed through thesecond casting mouth on the thus-peeled film on its surface that wascontacted with the support, for example as in JP-B 20235/1969.

[0262] The same or different cellulose acetate solutions may be cast infilm formation with no specific limitation. To make the formed multiplecellulose acetate films have the respective functions, the celluloseacetate solutions capable of giving the intended functions to the filmsshall be extruded out through the respective casting mouths.

[0263] If desired, the cellulose acetate solution may be co-cast alongwith any other solutions for other functional layers (e.g., adhesivelayer, colorant layer, antistatic layer, antihalation layer,UV-absorbent layer, polarizing layer) to form a laminate film.

[0264] In forming a single-layered film, it is necessary to extrude ahigh-concentration and high-viscosity cellulose acetate solution inorder that the film formed may have a desired thickness. In that case,however, the cellulose acetate solution is not stable and often forms asolid. This is problematic in that the solid causes fish eyes in thefilm formed, and the surface of the film is not smooth. To solve theproblem, multiple cellulose acetate solutions are cast through a castingmouth, and the resulting high-viscosity cellulose acetate solution isextruded onto a support to give a smooth and good film. Anotheradvantage is that the high-viscosity cellulose acetate solution reducesthe load of drying the film formed of it and its film-producing speedincreases.

[0265] A plasticizer may be added to the cellulose acetate film forimproving the mechanical properties of the film and for rapidly dryingthe film. For the plasticizer, usable are phosphates or carboxylates.Examples of the phosphates include triphenyl phosphate (TPP),biphenyldiphenyl phosphate (BDP) and tricresyl phosphate (TCP). Thecarboxylates are typically phthalates and citrates. Examples of thephthalates include dimethyl phthalate (DMP), diethyl phthalate (EDP),dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate(DPP) and diethylhexyl phthalate (DEHP). Examples of the citratesinclude triethyl o-acetylcitrate (OACTE) and tributyl o-acetylcitrate(OACTB). Examples of other carboxylates include butyl oleate,methylacetyl ricinoleate, dibutyl sebacate, and various trimellitates.Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferred foruse herein. More preferred are DEP and DPP.

[0266] The amount of the plasticizer that may be added to the filmpreferably falls between 0.1 and 25% by weight of cellulose acetate,more preferably between 1 and 20% by weight, most preferably between 3and 15% by weight.

[0267] Also if desired, an anti-aging agent (e.g., antioxidant,peroxide-degrading agent, radical inhibitor, metal inactivator, acidscavenger, amine) may be added to the cellulose acetate film. Suchanti-aging agents are described in JP-A199201/1991, 197073/1993,194789/1993, 271471/1993, 107854/1994. The amount of the anti-agingagent that may be added to the film preferably falls between 0.01 and 1%by weight of the film-forming solution (dope), more preferably between0.01 and 0.2% by weight. If its amount is smaller than 0.01% by weight,the anti-aging agent will be almost ineffective. However, if its amountis larger than 1% by weight, the anti-aging agent will bleed out of thefilm surface. Especially preferred examples of the anti-aging agent foruse herein are butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

[0268] One or both surfaces of the cellulose acetate film may be coatedwith a mat layer that comprises a matting agent and a polymer, forimproving the handlability of the film being produced. For the mattingagent and the polymer, preferred are the materials described in JP-A44327/1998. If desired, the matting agent may be added to the dope.

[0269] Many other additives may also be added to the cellulose acetatesolution, if desired, in any stage before or after or during itspreparation. The additives include, for example, UV absorbents; fineinorganic particles of, for example, silica, kaolin, talc, diatomaceousearth, quartz, calcium carbonate, barium sulfate, titanium oxide oralumina; thermal stabilizers such as alkaline earth metal salts with,for example, calcium or magnesium; other antistatic agents, flameretardants, lubricants, and oils.

[0270] Also if desired, a release promoter may be added to the film forreducing the load necessary in peeling the film. For it, for example,surfactants are effective, including, for example, phosphates,sulfonates, carboxylates, nonionic surfactants and cationic surfactants,to which, however, the release promoter usable herein is not limited.These are described, for example, in JP-A 243837/1986.

[0271] [Surface Treatment of Cellulose Acetate Film]

[0272] The cellulose acetate film may undergo surface treatment.Concretely, for it, the film is subjected to corona discharge treatment,glow discharge treatment, flame treatment, acid treatment, alkalitreatment or UV irradiation.

[0273] For ensuring the surface smoothness of the cellulose acetate filmthat undergoes such surface treatment, it is desirable that thetemperature at which the film receives the treatment is not higher thanthe glass transition point (Tg) of the film.

[0274] In case where the film is used for a transparent protective filmof polarizing plates, it is especially desirable that the film receivesacid or alkali treatment for increasing its adhesiveness to thepolarizing film of the plates. More preferably, the film receives alkalitreatment.

[0275] One preferred cycle of alkali treatment of the film comprisesdipping the film in an alkali solution, then neutralizing it in an acidsolution, rinsing it in water, and drying it.

[0276] The alkali solution may be a potassium hydroxide solution or asodium hydroxide solution. Of the solution, the hydroxide ion normalityconcentration preferably falls between 0.1 N and 3.0 N, more preferablybetween 0.5 N and 2.0 N. Preferably, the temperature of the alkalisolution falls between room temperature and 90° C., more preferablybetween 40° C. and 70° C. The alkali solution may be an aqueous solutionor a solution in an organic solvent. For the latter, the organic solventis preferably a lower alcohol, more preferably an alcohol having from 1to 5 carbon atoms or a glycol, even more preferably ethanol, n-propanol,iso-propanol, butanol, ethylene glycol or propylene glycol. Still morepreferred are iso-propanol and propylene glycol. If desired, these maybe mixed for use herein. In addition, water or surfactant may be addedto the solvent.

[0277] Some preferred examples of the solvent in which alkali isdissolved to be an alkali solution are mentioned belowiso-propanol/propylene glycol/water (70/15/15, by volume)iso-propanol/water (85/15, by volume) iso-propanol/propylene glycol(85/15, by volume) iso-propanol alone

[0278] The film may be dipped in the alkali solution, or may be coatedwith it (for example, through bar coating or curtain coating).

[0279] In the invention, for improving the adhesiveness of the celluloseacetate film to the layer that overlies it (e.g., adhesive layer,orientation film, optical anisotropic layer), an adhesive layer (subbinglayer) may be provided on the film, for example, as in JP-A 333433/1995.Preferably, the thickness of the adhesive layer falls between 0.1 μm and2 μm, more preferably between 0.2 μm and 1 μm.

[0280] [Polarizing Plate]

[0281] A polarizing plate comprises a polarizing film and twotransparent protective films provided on both surfaces of the polarizingfilm. In this, one protective film may be the cellulose acetate filmmentioned above or may be the optical compensating film of theinvention. The other protective film may be an ordinary celluloseacetate film; or both the protective films may be ordinary celluloseacetate films.

[0282] The polarizing film is, for example, an iodine-containingpolarizing film, a dichromatic dye-containing polarizing film, or apolyene polarizing film. For producing the iodine-containing polarizingfilm and the dye-containing polarizing film, generally used arepolyvinyl alcohol films.

[0283] The polymer films for these polarizing films are prepared, forexample, as follows: Using a tenter-type stretching machine, a polymerfilm is stretched under the condition that satisfies the followingrequirement (1) while it keeps its self-sustainability and while itsvolatile content is still at least 5%, and after thus stretched, thefilm is then shrunk to reduce its volatile content.

|L2−L1|>0.4W  (1)

[0284] wherein L1 indicates the trajectory of the film holder from thesubstantial holding start point of one edge of the film to thesubstantial holding release point thereof; L2 indicates the trajectoryof the film holder from the substantial holding start point of the otheredge of the film to the substantial holding release point thereof; and Windicates the distance between the two substantial holding releasepoints.

[0285]FIG. 7 is a schematic plan view showing a device for obliquelystretching a polymer film into a polarizing film of 45°-obliqueorientation. In this, (a) is a step of introducing an original polymerfilm in the direction of the arrow (Y); (b) is a step of stretching thefilm in the transverse direction; and (c) is a step of conveying thethus-stretched film to the subsequent step in the direction of the arrow(X). The film to be oriented is continuously introduced into the devicein the direction (Y), and it is first held by the left-side (seen fromthe upstream side) holder at the point B1. In this stage, the other edgeof the film is not held by the holder, and therefore the film receivesno tension in the transverse direction thereof. In other words, thepoint B1 is not a substantial holding start point. The substantialholding start point is defined as the point at which both edges of thefilm are held by the holder, and this includes two points A1 and C1, orthat is, the downstream holding start point A1 and the point C1 at whicha line that runs approximately perpendicularly to the center line 21 ofthe traveling film from the point A1 meets the trajectory 23 of theholder on the opposite side. Starting from this point, when the film isconveyed through the holder substantially in such a manner that its bothedges run substantially at the same speed, then the point A1time-dependently moves to A2, A3, . . . An, and the point C1 alsotime-dependently moves to C2, C3, . . . Cn. In this stage, the travelingfilm passes through the corresponding points An and Cn that are thebases of the holder at the same time, and the line that connects An toCn is the orientation direction of the film in which the film isoriented in that stage at An and Cn. As in FIG. 7, the points An aregradually delayed from the points Cn, and the orientation direction istherefore gradually inclined from the direction perpendicular to themachine direction. The substantial holding release point includes twopoints Cx and Ay, or that is, the upstream point Cx at which the filmseparates from the holder and the point Ay at which a line that runsapproximately perpendicularly to the center line 22 of the travelingfilm from the point Cx meets the trajectory 14 or 24 of the holder onthe opposite side. The angle of the final orientation of thethus-stretched film is defined by the ratio of the pathway differencebetween the right and left sides of the holder at the end point of thestretching process, Ay−Ax (that is, |L2−L1|) to the substantial outletwidth, Ay−Cx (that is, W). The tilt angle θ of the film orientationdirection to the film-traveling direction is represented by thefollowing:

tan θ=(Ay−Cx)/(Ay−Ax), or that is,

tan θ=|L1−L2|/W

[0286] After the point Ay, the upper edge of the film in the drawing isstill kept as it is up to 28. However, since the other edge of the filmis not held in this condition, the film is no more stretched in thetransverse direction thereof and the point 28 is not a substantialholding release point.

[0287] As in the above, the substantial holding start point is not apoint at which each edge of the film is merely engaged with thecorresponding side of the holder, but it includes two points. One is adownstream substantial engaging point, and the other is so defined thatthe line which connects the two substantial holding start points meetsthe center line of the traveling film approximately perpendicularlythereto at that point. Similarly, the substantial holding release pointincludes two. One is an upstream substantial release point, and theother is so defined that the line which connects the two substantialholding release points meets the centerline of the traveling filmapproximately perpendicularly thereto at that point. The condition thatthe line meets the center line of the traveling film approximatelyperpendicularly thereto is meant to indicate that the line that connectsthe two substantial holding start points or the two substantial holdingrelease points meets the center line of the film at an angle of 90±0.5°therebetween.

[0288] In case where the holder in the tenter-type stretching machine ismade to have a pathway difference between the right and left sidesthereof, the site at which both edges of the traveling film are firstheld by the holder on both sides thereof, or the site at which bothedges of the stretched film are finally released from the holder on bothsides thereto to the next stage often have a position error in themachine direction owing to some mechanical limitation, for example, onthe rail length of the machine. However, so far as the pathway from thesubstantial holding start point to the substantial holding release pointdefined as above satisfies the requirement (1), the film to be stretchedin the machine enjoys any desired position tolerance.

[0289] The tilt angle of the orientation axis of the stretched filmobtained in the above can be controlled, depending on the ratio of thesubstantial pathway difference between the right and left sides of theholder at the end point of the stretching process, |L1−L2|, to theoutlet width, W, in the step (c). Polarizing plates and phase-shiftfilms often require a film of 45°-orientation relative to the machinedirection. For orienting a film to have an orientation angle of around45°, the film stretching parameters preferably satisfy0.9W<|L1−L2|<1.1W, more preferably 0.97W<|L1−L2|<1.03W.

[0290] In reflection or transmission liquid crystal displays, theoriented cellulose acetate film is preferably so disposed that its phaselag axis crosses the transmission axis of the polarizing film thereinsubstantially at an angle of 45 degrees, though depending on the type ofthe liquid crystal displays.

[0291] [Liquid Crystal Display]

[0292] The optical compensating film of the cellulose acetate film, andthe polarizing plate (circularly polarizing plate) that comprises thecellulose acetate film are favorable to liquid crystal displays. Theyapply to any of transmission, reflection or semi-transmission liquidcrystal displays, but are more favorable to reflection orsemi-transmission liquid crystal displays.

[0293]FIG. 8 is a graphic view showing the basic constitution of thereflection liquid crystal display of the invention.

[0294] As in FIG. 8, the reflection liquid crystal display comprises alower substrate 11, a reflective electrode 12, a lower orientation film13, a liquid crystal layer 14, an upper orientation film 15, atransparent electrode 16, an upper substrate 17, a λ/4 plate 18 and apolarizing film 19 arrayed in that order from its bottom.

[0295] In this, the lower substrate 11 and the reflective electrode 12constitute a reflector. The lower orientation film 13 to the upperorientation film 15 constitute a liquid crystal cell. The λ/4 plate 18may be disposed in any site between the reflector and the polarizingfilm 19.

[0296] For displaying color images, the display shall have a colorfilter layer (not shown). The color filter layer is preferably betweenthe reflective electrode 12 and the lower orientation film 13, orbetween the upper orientation film 15 and the transparent electrode 16.

[0297] In the constitution of FIG. 8, a transparent electrode may beused in place of the reflective electrode 12 and an additional reflectormay be disposed therein. For the reflector to be combined with thetransparent electrode, preferred is a metal plate. If the reflector issmooth-faced, regular reflective components only are reflected thereonand the field of view is often narrowed. Therefore, it is desirable thatthe surface of the reflector is roughened (as in Japanese Patent275,620). In place of roughening the surface of the smooth-facedreflector, a light-diffusive film may be disposed on one side of thepolarizing film (on the side adjacent to the cell or on the outer sideof the film).

[0298] The liquid crystal cell is not specifically defined. For it, anyliquid crystal mode is employable with no specific limitation, butpreferred are TN (twisted nematic)-mode cells, STN (super twistednematic)-mode cells, HAN (hybrid aligned nematic)-mode cells, VA(vertically aligned)-mode cells, ECB (electrically controlledbirefringence)-mode cells and OCB (optically compensatory bend)-modecells.

[0299] Preferably, the twist angle in TN-mode liquid crystal cells fallsbetween 40 and 100°, more preferably between 50 and 90°, most preferablybetween 60 and 80°. The product (Δnd) of the refractivity anisotropy(Δn) of the liquid crystal layer and the thickness (d) thereofpreferably falls between 0.1 and 0.5 μm, more preferably between 0.2 and0.4 μm.

[0300] The twist angle in STN-mode liquid crystal cells preferably fallsbetween 180 and 360°, more preferably between 220 and 270°. The product(Δnd) of the refractivity anisotropy (Δn) of the liquid crystal layerand the thickness (d) thereof preferably falls between 0.3 and 1.2 μm,more preferably between 0.5 and 1.0 μm.

[0301] In HAN-mode liquid crystal cells, it is desirable that the liquidcrystal on one substrate is substantially vertically oriented and thepre-tilt angle of the liquid crystal on the other substrate is from 0 to45°. The product (Δnd) of the refractivity anisotropy (Δn) of the liquidcrystal layer and the thickness (d) thereof preferably falls between 0.1and 1.0 μm, more preferably between 0.3 and 0.8 μm. The substrate onwhich the liquid crystal is vertically oriented may be on the side ofthe reflector, or on the side of the transparent electrode.

[0302] In VA-mode liquid crystal cells, the rod liquid-crystallinemolecules are substantially vertically oriented with no voltage appliedthereto. VA-mode liquid crystal cells include (1) those in the narrowsense of the word in which the rod liquid-crystalline molecules aresubstantially vertically oriented with no voltage applied thereto, butare substantially horizontally oriented with voltage applied thereto (asin JP-A176625/1990, JP-B69536/1995), and (2) those of multi-domainVA-mode that have the advantage of enlarged view angles. Concretely, theVA-mode liquid crystal cells (2) include MVA (SID97, described in Digestof Tech. Papers (preliminary), 28, (1997), 845; SID99 in Digest of Tech.Papers (preliminary), 30, (1999), 206, and JP-A258605/1999; SURVAILVAL(in Monthly Display, Vol. 6, No. 3 (1999), 14); PVA (in Asia Display 98,Proc. of the 18th Inter. Display Res. Conf. (preliminary) (1998), 383);Para-A (announced in LCD/PDP International '99); DDVA (SID98, in Digestof Tech. Papers (preliminary), 29, (1998), 845); EOC (SID98, in Digestof Tech. Papers (preliminary), 29, (1998), 313); PSHA (SID98, in Digestof Tech. Papers (preliminary), 29, (1998), 1081); RFFMA (in Asia Display98, Proc. of the 18th Inter. Display Res. Conf. (preliminary) (1998),337583); HMD (SID98, in Digest of Tech. Papers (preliminary), 29,(2998), 720). Apart from these, VA-mode liquid crystal cells furtherinclude (3) those in which the rod liquid-crystalline molecules aresubstantially vertically oriented with no voltage applied thereto, andare oriented in a mode of twisted multi-domain (n-ASM mode) with voltageapplied thereto (as in IWD '98, Proc. of the 5th Inter. Display Workshop(preliminary) (1998), 143).

[0303] In OCB-mode liquid crystal cells, the rod liquid-crystallinemolecules are substantially oppositely (symmetrically) oriented in theupper and lower parts of the liquid crystal cell. Having theconstitution, the cells have a function of self-optical compensation.Their details are described in U.S. Pat. Nos. 4,583,825, 5,410,422.

[0304] ECB-mode liquid crystal cells are characterized in that theliquid crystal molecules therein are horizontally oriented, and theirdetails are described in JP-A 203946/1993.

[0305] Reflection and semi-transmission liquid crystal displays areusable in any normally white mode that gives light display images underlow voltage but gives dark display images under high voltage and in anynormally black mode that gives dark display images under low voltage butgives light display images under high voltage, but are more favorable tonormally white mode devices.

[0306] [Application to Touch Panel and Organic EL Displays]

[0307] The optical compensating film of the invention is applicable totouch panels such as those in JP-A 127822/1993, 48913/2002.

[0308] The optical compensating film of the invention is also applicableto organic EL displays such as those in JP-A 305729/1999, 307250/1999,267097/2000.

EXAMPLES

[0309] Examples of the invention are described below, to which, however,the invention is not limited.

[0310] (1) Measurement of Haze:

[0311] The haze of each cellulose acetate film (optical compensatingfilm) produced is measured with a haze meter (NDH1001-DP, from NipponDenshoku Kogyo). Concretely, five random points of one sample aremeasured, and their data are averaged to be the haze of the sample.

[0312] (2) Measurement of Water Content:

[0313] The water content of each sample is measured according to theCurl-Fisher method, which is as follows:

[0314] (i) The sample to be measured (0.9 m×4.5 cm, two sheets) isweighed.

[0315] Water on the surfaces of wet samples is rapidly removed.Immediately after its sampling, the sample is put into a ground stopperbottle of glass, and is carried to a moisture meter. Within 3 minutesafter its sampling, the water content of the sample is measured.

[0316] (ii) Using a moisture meter mentioned below, the water content ofthe sample is measured.

[0317] Using an evaporator, Mitsubishi Chemical's VA-05 Model, water inthe sample was evaporated away at 150° C. and introduced into a moisturemeter.

[0318] Using a moisture meter, Curl-Fisher Moisture Meter (MitsubishiChemical's CA-03 Model), the amount of water introduced thereinto fromthe evaporator is measured.

[0319] (iii) Computation of water content:

[0320] The water content of the sample is computed as follows:

Water content(%)=0.1×(W/F)

[0321] in which W is the water content (μg) indicated by the moisturemeter and F is the weight (mg) of the sample.

[0322] (3) Water Film on Cellulose Acetate Film:

[0323] Filter paper is pressed against the cellulose acetate film justbefore stretched, and the area of the filter paper having absorbed waterfrom the film to change its color is measured. The area thus measured isdivided by the overall area of the filter paper, and it is representedin terms of percentage.

[0324] (4) Measurement of Retardation and NZ Factor:

[0325] The retardation and the NZ factor of each optical compensatingfilm are measured as follows:

[0326] (i) Re450, Re550, Re590: Using an automatic birefringencerefractometer (KOBRA-21ADH/PR, from Oji Test Instruments), theretardation value of the sample film is measured with a ray of 450 nm,550 nm or 590 nm applied in the direction perpendicular to the filmsurface.

[0327] (ii) NZ factor ((nx−nz)/(nx−ny)):

[0328] Using an automatic birefringence refractometer (KOBRA-21ADH/PR,from Oji Test Instruments), the retardation of the sample film ismeasured with a ray of 550 nm applied in the direction inclined by 40degrees or −40 degrees from the direction perpendicular to the filmsurface, and Re(0), Re(4) and Re(−40) are obtained. From these, obtainedare the refractive index, nx, in the direction of the phase lag axis ofthe film, the refractive index, ny, in the direction perpendicular tothe in-plane phase lag axis of the film, and the refractive index, nz,in the direction of the thickness of the film. From the thus-obtaineddata, the value of (nx−nz)/(nx−ny) is computed.

[0329] (5) Measurement of Degree of Acetyl Substitution:

[0330] According to the method described in Polymer Journal 17,1065-1069 (1985), the degree of acetyl substitution of each sample ismeasured through ¹³C-NMR spectrometry.

[0331] (Formation of Cellulose Acetate Film 1)

[0332] A cellulose acetate solution having the composition mentionedbelow was prepared. Composition of Cellulose Acetate Solution Celluloseacetate (degree of acetylation, 60.9%)   100 wt. pts. Triphenylphosphate (plasticizer)  10.0 wt. pts. Biphenyldiphenyl phosphate(plasticizer)  5.0 wt. pts. Methylene chloride (first solvent) 565.6 wt.pts. Methanol (second solvent)  49.2 wt. pts. Retardation-controllingagent  1.97 wt. pts. Silica particles (20 nm)  0.05 wt. pts.

[0333] For the retardation-controlling agent, used was the following rodcompound:

[0334] The UV and visible (UV-vis) spectrum of theretardation-controlling agent was measured according to the methodmentioned above. It gave an absorption maximum at a wavelength (λmax) of230 nm and its absorption coefficient (ε) was 16000.

[0335] The resulting dope was cast on a film-forming band, and dried atroom temperature for 1 minute and then at 45° C. for 5 minutes. Afterdried, the amount of the solvent still remaining in the film was 30% byweight. The cellulose acetate film was peeled from the band, and driedat 100° C. for 10 minutes and then at 130° C. for 20 minutes. This iscellulose acetate film 1. The amount of the solvent still remaining inthe film 1 was 0.1% by weight, and the film thickness was 130 μm.

[0336] (Formation of Cellulose Acetate Film 2)

[0337] A cellulose acetate solution having the composition mentionedbelow was prepared. Composition of Cellulose Acetate Solution Celluloseacetate (degree of acetylation, 60.9%)   100 wt. pts. Triphenylphosphate (plasticizer)  10.0 wt. pts. Biphenyldiphenyl phosphate(plasticizer)  5.0 wt. pts. Methylene chloride (first solvent) 534.9 wt.pts. Methanol (second solvent)  79.9 wt. pts. Retardation-controllingagent  1.97 wt. pts. Silica particles (20 nm)  0.05 wt. pts.

[0338] The retardation-controlling agent used herein is the same as thatused in the cellulose acetate film 1.

[0339] The resulting dope was cast on a film-forming band, and dried atroom temperature for 1 minute and then at 45° C. for 5 minutes. Afterdried, the amount of the solvent still remaining in the film was 30% byweight. The cellulose acetate film was peeled from the band, and driedat 100° C. for 10 minutes and then at 130° C. for 20 minutes. This iscellulose acetate film 2. The amount of the solvent still remaining inthe film 2 was 0.1% by weight, and the film thickness was 130 μm.

[0340] (Formation of Cellulose Acetate Film 3)

[0341] A cellulose acetate solution having the composition mentionedbelow was prepared. Composition of Cellulose Acetate Solution Celluloseacetate (degree of acetylation, 60.9%)   100 wt. pts. Triphenylphosphate (plasticizer)  10.0 wt. pts. Biphenyldiphenyl phosphate(plasticizer)  5.0 wt. pts. Methylene chloride (first solvent) 534.9 wt.pts. Methanol (second solvent)  79.9 wt. pts. Retardation-controllingagent  1.97 wt. pts. Silica particles (20 nm)  0.05 wt. pts.

[0342] For the retardation-controlling agent, used was the followingtabular compound.

[0343] The resulting dope was cast on a film-forming band, and dried atroom temperature for 1 minute and then at 45° C. for 5 minutes. Afterdried, the amount of the solvent still remaining in the film was 30% byweight. The cellulose acetate film was peeled from the band, and driedat 100° C. for 10 minutes and then at 130° C. for 20 minutes. This iscellulose acetate film 3. The amount of the solvent still remaining inthe film 3 was 0.1% by weight, and the film thickness was 130 μm.

[0344] (Formation of Cellulose Acetate Film 4)

[0345] A cellulose acetate solution having the composition mentionedbelow was prepared. Composition of Cellulose Acetate Solution Cellulosetriacetate (degree of acetylation, 60.3%)   20 wt. pts. Methyl acetate  58 wt. pts. Acetone   5 wt. pts. Methanol   5 wt. pts. Ethanol   5 wt.pts. Butanol   5 wt. pts. Retardation-controlling agent  1.0 wt. pt.Plasticizer A (ditrimethylolpropane tetraacetate)  1.2 wt. pts.Plasticizer B (triphenyl phosphate)  1.2 wt. pts. UV absorbent a:2,4-bis (n-octylthio-6-(4-hydroxy-3,5-di-tert-  0.2 wt. ptsbutylanilino)-1,3,5-triazine UV absorbent b:2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-  0.2 wt. pts.chlorobenzotriazole UV absorbent c:2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)-5-  0.2 wt. ptschlorobenzotriazole C₁₂H₂₅OCH₂CH₂O—P(═O)—(OK)₂ (release agent) 0.02 wt.pts Citric acid (release agent) 0.02 wt. pts. Silica particles (particlesize, 20 nm; Mohs hardness, about 0.05 wt. pts. 7)

[0346] The retardation-controlling agent used herein is the same as thatused in the cellulose acetate film 1. In the cellulose acetate usedherein, the 6-position is acetylated to a higher degree than the 2- and3-positions. In this, the degree of acetylation at the 6-, 2- and3-positions is 20.5%, 19.9% and 19.9%, respectively.

[0347] The constitutive components were dissolved according to a coolingdissolution method mentioned below. Concretely, the compounds weregradually added to the solvent with full stirring, and then left at roomtemperature (25° C.) for 3 hours for which the compounds well swelled.With gradually stirring it, the resulting swollen mixture was cooled to−30° C. at a rate of −8° C./min, and then to −70° C. After 6 hours, thiswas then heated at a rate of +8° C./min. In the stage when this formed asol in some degree, stirring it was started. This was further heated upto 50° C. to obtain a dope.

[0348] The resulting dope was cast on a film-forming band, and dried atroom temperature for 1 minute and then at 45° C. for 5 minutes. Afterdried, the amount of the solvent still remaining in the film was 30% byweight. The cellulose acetate film was peeled from the band, and driedat 100° C. for 10 minutes and then at 130° C. for 20 minutes. This iscellulose acetate film 4. The amount of the solvent still remaining inthe film 4 was 0.1% by weight, and the film thickness was 130 μm.

[0349] (Preliminary Experiment 1 for Film to Absorb Water)

[0350] The cellulose acetate film 1 formed in the above was dipped in awater thermostat at 80° C., and it was analyzed in point of the relationbetween the dipping time and the water content of the film. Dipped inwater for 0 minute, 1 minute, 2 minutes, 4 minutes, 8 minutes and 20minutes, the water content of the film was 1.89% by weight, 3.78% byweight, 4.21% by weight, 4.53% by weight, 4.79% by weight and 4.83% byweight, respectively. The other cellulose acetate films 2 to 4 were alsoanalyzed in the same manner as above in point of the dipping time andthe water content thereof. The results of these films were almost thesame as those of the film 1.

[0351] (Preliminary Experiment 2 for Film to Absorb Water)

[0352] The cellulose acetate film 1 formed in the above was put in ahigh-humidity thermostat at 80° C. and 95% RH, and it was analyzed inpoint of the relation between the moisturizing time and the watercontent of the film. Moisturized for 0 minute, 1 minute, 2 minutes, 4minutes, 8 minutes and 20 minutes, the water content of the film was1.89% by weight, 2.91% by weight, 3.25% by weight, 3.54% by weight,3.57% by weight and 3.56% by weight, respectively. The other celluloseacetate films 2 to 4 were also analyzed in the same manner as above inpoint of the moisturizing time and the water content thereof. Theresults of these films were almost the same as those of the film 1.

Example 1

[0353] (Formation of Optical Compensating Film 1)

[0354] The cellulose acetate film 1 formed in the above was dipped in awater thermostat at 80° C. for 5 minutes. Thus dipped, the film absorbedwater to have a water content of 4.63% by weight. Then, this was putinto an air thermostat at 90° C., and then immediately stretched by42.5%. This was stretched in a clip-to-clip stretching method, in whichthe aspect ratio (L/W) was 0.8 and the stretching time was 9 seconds.Immediately after stretched, the water content of the film was 4.7% byweight. Next, this was dried in a thermostat at 80° C. for 3 minutes,and then conditioned at 25° C. and 60% RH for at least 2 hours. Theoptical properties of the film were measured, and the data obtained aregiven in Table 1. After stretched, the thickness of the film was 115 μm.

Example 2

[0355] (Formation of Optical Compensating Film 2)

[0356] The cellulose acetate film 1 formed in the above was dipped in awater thermostat at 80° C. for 5 minutes. Thus dipped, the film absorbedwater to have a water content of 4.63% by weight. Then, this was putinto a high-humidity thermostat at 70° C. and 95% RH, and thenimmediately stretched by 35%. This was stretched in a clip-to-clipstretching method, in which the stretch aspect ratio (L/W) was 0.8 andthe stretching time was 7 seconds. Immediately after stretched, thewater content of the film was 4.8% by weight. After taken out, the filmwas dried in a thermostat at 80° C. for 3 minutes, and then conditionedat 25° C. and 60% RH for at least 2 hours. The optical properties of thefilm were measured, and the data obtained are given in Table 1. Afterstretched, the thickness of the film was 117 μm.

Example 3

[0357] (Formation of Optical Compensating Film 3)

[0358] The cellulose acetate film 1 formed in the above was dipped in awater thermostat at 80° C. for 5 minutes. Thus dipped, the film absorbedwater to have a water content of 4.63% by weight. Then, this was putinto a high-humidity thermostat at 70° C. and 95% RH, and thenimmediately stretched by 42.5%. This was stretched in a clip-to-clipstretching method, in which the stretch aspect ratio (L/W) was 1.0 andthe stretching time was 9 seconds. Immediately after stretched, thewater content of the film was 4.8% by weight. After taken out, the filmwas dried in a thermostat at 80° C. for 3 minutes, and then conditionedat 25° C. and 60% RH for at least 2 hours. The optical properties of thefilm were measured, and the data obtained are given in Table 1. Afterstretched, the thickness of the film was 115 μm.

Example 4

[0359] (Formation of Optical Compensating Film 4)

[0360] The cellulose acetate film 1 formed in the above was put in ahigh-humidity thermostat at 80° C. and 95% RH for 5 minutes. Thus puttherein, the film absorbed water to have a water content of 3.55% byweight, and it was stretched by 45.0%. This was stretched in aclip-to-clip stretching method, in which the stretch aspect ratio (L/W)was 1.0 and the stretching time was 9 seconds. Immediately afterstretched, the water content of the film was 4.8% by weight. After takenout, the film was dried in a thermostat at 80° C. for 3 minutes, andthen conditioned at 25° C. and 60% RH for at least 2 hours. The opticalproperties of the film were measured, and the data obtained are given inTable 1. After stretched, the thickness of the film was 115 μm.

Example 5

[0361] (Formation of Optical Compensating Film 5)

[0362] The cellulose acetate film 1 formed in the above was put in ahigh-humidity thermostat at 80° C. and 95% RH for 5 minutes. Thus puttherein, the film absorbed water to have a water content of 3.55% byweight. Then, this was stretched by 45.0% while exposed to high-pressurewater vapor at 120° C. for 2 seconds. This was stretched in aclip-to-clip stretching method, in which the stretch aspect ratio (L/W)was 1.0 and the stretching time was 9 seconds. Immediately afterstretched, the water content of the film was 3.7% by weight. After takenout, the film was dried in a thermostat at 80° C. for 3 minutes, andthen conditioned at 25° C. and 60% RH for at least 2 hours. The opticalproperties of the film were measured, and the data obtained are given inTable 1. After stretched, the thickness of the film was 115 μm.

Comparative Example 1

[0363] (Formation of Optical Compensating Film 6)

[0364] The cellulose acetate film 1 formed in the above was put in athermostat at 130° C. for 5 minutes. Thus put therein, the film had awater content of 0.4% by weight, and then it was stretched by 37%. Thiswas stretched in a clip-to-clip stretching method, in which the stretchaspect ratio (L/W) was 3.3. Then, the film was conditioned at 25° C. and60% RH for at least 2 hours. The optical properties of the film weremeasured, and the data obtained are given in Table 1. After stretched,the thickness of the film was 115 μm. TABLE 1 Example 1 Example 2Example 3 Example 4 Example 5 Comp. Ex. 1 Draw Ratio 42.5% 35.0% 42.5%45.0% 45.0% 37.0% Re450 [nm] 128 106 129 121 123 124 Re550 [nm] 142 118143 134 137 138 Re590 [nm] 145 120 146 137 140 141 (nx − nz)/ 1.62 1.851.66 1.76 1.60 1.32 (nx − ny) (NZ factor) Haze 0.3 0.4 2.0 0.4 0.5 0.4

[0365] The other cellulose acetate films 2 to 4 formed in the above wereprocessed in the same manner as in Examples 1 to 5 into opticalcompensating films, all of which had almost the same data as in Table 1.

Example 6

[0366] (Fabrication of Circularly Polarizing Plates)

[0367] A PVA film was dipped in an aqueous solution of iodine (2.0g/liter) and potassium iodide (4.0 g/liter) at 25° C. for 240 seconds,and then in an aqueous solution of boric acid (10 g/liter) at 25° C. for60 seconds. Then, this was introduced into a tenter-type stretchingmachine as in FIG. 7, and stretched 5.3-fold therein. The tenter in themachine is so designed that it bends in the machine direction as in FIG.7, and after the bent zone, its width is kept constant. After dried inan atmosphere at 80° C., the stretched film was taken out of the tenter.The film-traveling speed difference between the tenter clips on bothsides of the tenter was smaller than 0.05%, and the angle of thecenterline of the film just having been introduced into the tenter tothe centerline of the stretched film to be fed to the next stage was46°. In this step, |L1−L21 was 0.7 m and W was 0.7 m, or that is,|L1−L21=W. At the tenter outlet, the tilt angle of the substantialstretched direction, Ax−Cx, of the film to the centerline 22 of thestretched film to be fed to the next stage was 45°. At the tenteroutlet, neither film shrinkage nor film deformation was found. Using anadhesive of aqueous 3% PVA (Kuraray's PVA-117H) solution, a saponifiedfilm of Fuji Photo Film's Fujitac (cellulose triacetate having aretardation value of 3.0 nm), and the optical compensating film 4 ofExample 4 that had been saponified on its one surface were laminatedwith the polarizing film prepared herein, in a mode of roll-to-rolllamination where the adhesive-coated surface of each film was kept incontact with the polarizing film. The process gave a circularlypolarizing plate. The same process, in which, however, the opticalcompensating film 5 of Example 5 that had been saponified in the samemanner on its one surface was used in place of the optical compensatingfilm 4, also gave a circularly polarizing plate.

[0368] The optical properties of the circularly polarizing plates thusfabricated herein were measured. Both the circularly polarizing platesattained almost complete circular polarization in a broad wavelengthrange (450 to 590 nm).

Example 7

[0369] (Fabrication of TN-mode Reflection Liquid Crystal Displays)

[0370] A glass substrate with an ITO transparent electrode mountedthereon, and a glass substrate with a surface-roughened, reflectivealuminium electrode mounted thereon were prepared. An orientation filmof polyimide (SE-7992 from Nissan Chemical) was formed on the electrodeof each of the two glass substrates, and rubbed. Via a 1.7 μm-spacer puttherebetween, the two substrates were stacked with their orientationfilms facing each other. In stacking them, the two substrates were socontrolled that the rubbing directions of the two orientation filmsthereon cross at an angle of 110°. A liquid crystal (MLC-6252 fromMerck) was introduced into the space between the substrates to form aliquid crystal layer therebetween. The process gave a TN-mode liquidcrystal cell having a twist angle of 70° and a value Δnd of 269 nm.

[0371] Any of the two circularly polarizing plates that had beenfabricated in Example 6 (each laminated with a protective film of whichthe surface had been AR-processed) was stuck to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof, in such a manner that the cellulose acetate film ofthe polarizing plate faces the substrate.

[0372] A rectangular wave voltage of 1 kHz was applied to thethus-fabricated, reflection liquid crystal display. The display wasvisually checked at 1.5 V for white expression and 4.5V for blackexpression. It was confirmed that both the white expression and theblack expression were neutral gray with no other color.

[0373] Next, using a contrast meter (EZ Contrast 160D from Eldim), thecontrast ratio of the reflection brightness of the display was measured.The contrast ratio in front of the display was 25, and the field of view(view angle) to give a contrast ratio of 10 was at least 120° in thevertical direction and at least 120° in the horizontal direction. In adurability test at 60° C. and 90% RH for 500 hours, the display was goodwith no problem of expression.

Example 8

[0374] (Fabrication of STN-Mode Reflection Liquid Crystal Displays)

[0375] A glass substrate with an ITO transparent electrode mountedthereon, and a glass substrate with a smooth reflective aluminiumelectrode mounted thereon were prepared. An orientation film ofpolyimide (SE-150 from Nissan Chemical) was formed on the electrode ofeach of the two glass substrates, and rubbed. Via a 6.0 μm-spacer puttherebetween, the two substrates were stacked with their orientationfilms facing each other. In stacking them, the two substrates were socontrolled that the rubbing directions of the two orientation filmsthereon cross at an angle of 60°. A liquid crystal (ZLI-2977 from Merck)was introduced into the space between the substrates to form a liquidcrystal layer therebetween. The process gave an STN-mode liquid crystalcell having a twist angle of 2400 and a value Δnd of 791 nm.

[0376] Using an adhesive, an internal diffusive sheet (IDS fromDai-Nippon Printing) and any of the two circularly polarizing platesthat had been fabricated in Example 6 were stuck in that order to theITO transparent electrode-having glass substrate on its side opposite tothe side of the electrode thereof, in such a manner that the polarizingplate is the outermost layer.

[0377] A rectangular wave voltage of 55 Hz was applied to thethus-fabricated, reflection liquid crystal display. The display wasvisually checked at 2.0 V for black expression and at 2.5 V for whiteexpression. It was confirmed that both the white expression and theblack expression were neutral gray with no other color.

[0378] Next, using a contrast meter (EZ Contrast 160D from Eldim), thecontrast ratio of the reflection brightness of the display was measured.The contrast ratio in front of the display was 8, and the field of view(view angle) to give a contrast ratio of 3 was 90° in the verticaldirection and 105° in the horizontal direction.

Example 9

[0379] (VA-mode Liquid Crystal Displays)

[0380]FIG. 9 is a cross-sectional view showing the basic constitution ofa VA-mode liquid crystal display. As in FIG. 9, the VA-mode liquidcrystal display illustrated comprises a lower glass substrate 41, aninsulation film 39, a thin-film transistor 38, a reflector 36, a lowerorientation film 35, a liquid crystal 40, an upper orientation film 34,an ITO transparent electrode 33, an overcoat layer 33, a color filter 31and an upper glass substrate 30 arrayed in that order from its bottom.

[0381] A glass substrate 30 with an ITO transparent electrode 33 mountedthereon, and a glass substrate 41 with a surface-roughened, reflectivealuminium electrode 35 to 39 mounted thereon were prepared. Verticalorientation films (RN783 from Nissan Chemical) were prepared for theupper orientation film 34 and the lower orientation film 35, and theywere rubbed. Via a 1.7 μm-spacer put therebetween, the two substrateswere stacked with their orientation films facing each other. In stackingthem, the two substrates were so controlled that the rubbing directionsof the two orientation films thereon cross at an angle of 110°. A liquidcrystal having Δn=0.08 and Δε=−4 (from Merck) was introduced throughvacuum injection into the space between the substrates to form a liquidcrystal layer (40) therebetween. The process gave a VA-mode liquidcrystal cell having a twist angle of 45° and a value Δnd of 135 nm.

[0382] Using an adhesive, the optical compensating film formed inExample 4, and a commercially-available polarizing plate (HLC2-5618HCSfrom Sanritz) were stuck in that order to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof. In sticking the optical compensating film and thepolarizing plate to the substrate, they were so controlled that theabsorption axis of the polarizing plate crosses the phase lag axis ofthe optical compensating film at an angle of 45 degrees. The devicesthus fabricated herein to have the optical compensating film 4 ofExample 4 all had a broad field of view, concretely having a view angleof at least 160 degrees in the vertical direction and a view angle of atleast 160 degrees in the horizontal direction. In place of the opticalcompensating film 4 of Example 4, the optical compensating film 5 ofExample 5 was used to fabricate the devices of the same constitution asherein. Thus fabricated, all the devices also had a broad field of view,concretely having a view angle of at least 160 degrees in the verticaldirection and a view angle of at least 160 degrees in the horizontaldirection. However, when the optical compensating film 6 formed inComparative Example 1 was used, the view angle of the devices was notlarger than 140 degrees in both the vertical direction and thehorizontal direction.

[0383] A VA-mode liquid crystal cell was formed in the same manner asherein, and the circularly polarizing plate formed in Example 6 wasstuck to the ITO transparent electrode-having glass substrate on itsside opposite to the side of the electrode thereof, using an adhesive.Thus fabricated, the device also had a broad field of view, concretelyhaving a view angle of at least 160 degrees in the vertical directionand a view angle of at least 160 degrees in the horizontal direction.

[0384] As demonstrated herein, the angle dependency of the birefringence(Δn) of liquid crystal cells varies depending on the liquid crystalpanels combined with the cells, and the view angle characteristic ofliquid crystal displays could not be optimized by merely controlling Re.It is understood from the data in this example that the matter ofimportance for the view angle characteristic optimization in fabricatingliquid crystal displays is to control the NZ factor of the opticalcompensating film used, not varying Re thereof.

Example 10

[0385] (ECB-Mode Liquid Crystal Displays)

[0386] According to the process of Example 1 in JP-A 316378/1999,circularly polarizing plates were fabricated in which, however, theoptical compensating films 4, 5 and 6 that had been formed in Examples 4and 5 and Comparative Example 1, respectively, were used for the secondtransparent support. When the optical compensating film was stuck to thepolarizing film, they were so controlled that the absorption axis of thepolarizing film crosses the phase lag axis of the optical compensatingfilm at an angle of 45 degree. Using the circularly polarizing platesthus fabricated herein, ECB-mode liquid crystal displays wereconstructed according to the process of Example 6 in JP-A 316378/1999.The devices comprising the optical compensating film of the inventionall had a broad field of view, concretely having a view angle of atleast 120 degrees in the vertical direction and a view angle of at least115 degrees in the horizontal direction. However, the devices comprisingthe optical compensating film of Example 1 were not so good, concretelyhaving a view angle of not larger than 100 degrees in both the verticaldirection and the horizontal direction.

Example 11

[0387] (Organic EL Device-Having Displays)

[0388] According to JP-A 267097/2000, a display having a constitution ofprotective tack (provided with an antireflection layer on its outermostsurface)/polarizing film/optical compensating film/organic ELdevice/reflective electrode arrayed in that order from the side ofviewers was fabricated, in which the optical compensating film 4 or 5formed in Examples 4 or 5 was used. In this, the polarizing film and theoptical compensating film were so arrayed that the transmission axis ofthe former crosses the phase lag axis of the latter at an angle of 45°.Thus fabricated, the display was visually checked for its colorexpression. It was confirmed that the black expression in the display iscolored little, and therefore the contrast of the display is high andthe visibility thereof is good.

Example 12

[0389] (Packaging in Semi-Transmission Devices)

[0390] Cybershot (from Sony) was modified as follows: The polarizingplate, the λ/2 plate and the λ/4 plate in the upper part of the liquidcrystal cell in the liquid crystal display unit were peeled off. Usingan adhesive, the optical compensating film 4 or 5 (λ/4 plate) formed inExample 4 or 5, and a commercially-available polarizing plate(HLC2-5618HCS from Sanritz) were laminated in that order on the glasssubstrate. In laminating the optical compensating film and thepolarizing film on the substrate, they were so controlled that theabsorption axis of the polarizing film crosses the phase lag axis of theoptical compensating film at an angle of 45 degrees. The devicescomprising the optical compensating film 4 or 5 of Examples 4 or 5 allhad a broad field of view, concretely having a view angle of at least120 degrees in the vertical direction and a view angle of at least 115degrees in the horizontal direction.

Comparative Example 2

[0391] In the same manner as in Example 12, the device was modified, forwhich, however, used was the optical compensating film 6 formed inComparative Example 1. The thus-modified device was inferior to those ofExample 12 in point of the field of view. Concretely, its view angle was100 degrees in the vertical direction and 100 degrees in the horizontaldirection.

Example 13

[0392] (Packaging in Reflection Liquid Crystal Displays)

[0393] A tough panel-having reflection liquid crystal display (Sharp'sZaurus) was modified as follows: The polarizing plate and the opticalcompensating film in the structure of touch panel/polarizingplate/optical compensating film/liquid crystal cell of the display werepeeled off and replaced with the optical compensating film 4 or 5 ofExample 4 or 5 and a commercially-available polarizing plate(HLC2-5618HCS from Sanritz). For this, the polarizing plate and theoptical compensating film were so controlled that the absorption axis ofthe former crosses the phase lag axis of the latter at an angle of 45degrees. This is for maximizing the contrast of the modified device.Thus modified, the liquid crystal displays having the opticalcompensating film 4 or 5 of Example 4 or 5 had a broad field of view,concretely having a view angle of at least 120 degrees in the verticaldirection and a view of angle of at least 115 degrees in the horizontaldirection.

Comparative Example 3

[0394] In the same manner as in Example 13, the device was modified, forwhich, however, used was the optical compensating film 6 formed inComparative Example 1. The thus-modified device was inferior to those ofExample 13 in point of the field of view. Concretely, its view angle was100 degrees in the vertical direction and 100 degrees in the horizontaldirection.

Example 14

[0395] 1. Formation of Optical Compensating Films (Stretched CelluloseAcetate Films):

[0396] (1) Composition:

[0397] A cellulose acetate dope (high-concentration solution) having thecomposition mentioned below was prepared. In this, the rod compound orthe tabular compound mentioned above was used for theretardation-controlling agent (aromatic compound having at least twoaromatic rings).

[0398] (a) Methylene Chloride (MC)-Based Composition: Cellulose acetate(its degree of acetylation is in Table   100 wt. pts. 2) Triphenylphosphate   10 wt. pts. Biphenyldiphenyl phosphate    5 wt. pts.Methylene chloride 565.6 wt. pts. Methanol  49.2 wt. pts.Retardation-controlling agent (Re-controlling agent) as in Table 2Silica particles (particle size, 20 nm)  0.05 wt. pts.

[0399] (β) Methyl Acetate (MA)-Based Composition: Cellulose acetate (itsdegree of acetylation is in Table   118 wt. pts. 2) Triphenyl phosphate 9.19 wt. pts. Biphenyldiphenyl phosphate  4.60 wt. pts. Tribenzylamine 2.36 wt. pts. Methyl acetate   530 wt. pts. Ethanol  99.4 wt. ptsButanol  33.1 wt. pts. Methylene chloride 565.6 wt. pts.Retardation-controlling agent (Re-controlling agent) as in Table 2Silica particles (particle size, 20 nm)  0.05 wt. pts.

[0400] (2) Dissolution:

[0401] The MC-based composition was dissolved in a room-temperaturedissolution method; and the MA-based composition was in a coolingdissolution method. The two gave two different dopes.

[0402] (a) Room-Temperature Dissolution Method:

[0403] With well stirring, the above-mentioned compounds were graduallyadded to the solvent, and left at room temperature (25° C.) for 3 hoursfor which they well swelled. The resulting swollen mixture was put intoa mixer tank equipped with a reflex condenser, and dissolved withstirring at 50° C.

[0404] (b) Cooling Dissolution Method:

[0405] With well stirring, the above-mentioned compounds were graduallyadded to the solvent, and left at room temperature (25° C.) for 3 hoursfor which they well swelled. With gradually stirring, the resultingswollen mixture was cooled to −30° C. at a rate of −8° C./min, and thento −70° C. After 6 hours, this was then heated at a rate of +8° C./min.In the stage when this formed a sol in some degree, stirring it wasstarted. This was further heated up to 50° C. to obtain a dope.

[0406] (3) Film Formation:

[0407] The dope was formed into a film according to any of the followingtwo modes, as in Table 2.

[0408] (a) Single-Layer Film Formation:

[0409] The solution (dope) obtained in the method as above was filteredthrough filter paper (Azumi Filter's No. 244) and through flannel cloth,then fed into a pressure die via a metering gear pump. Using a castingmachine with a band having an effective length of 6 m, this was cast onthe band so that its final thickness after dried and stretched could beas in Table 2. The band temperature was 0° C. Thus cast, the film wasexposed to air fro 2 seconds to dry it. When the volatile content of thefilm reached 50% by weight, the film was peeled off from the band. Then,this was stepwise dried at 100° C. for 3 minutes, at 130° C. for 5minutes and at 160° C. for 5 minutes, not fixed but allowed to freelyshrink. Thus dried, the solvent remaining in the film was reduced to atmost 1%.

[0410] (β) Multi-Layer Film Formation:

[0411] Using a three-layer co-casting die unit, the dope having thecomposition as above was cast through the center die on a metal supportwhile, at the same time, the dope having been diluted to have anincreased solvent content of 10% by weight was through the two outerdies thereon to. Thus co-cast, the multi-layer film was peeled off fromthe support and dried. This is a three-layered cellulose acetate filmlaminate of the invention (thickness of the inner layer/thickness ofeach surface layer=8/1). This was stepwise dried at 70° C. for 3 minutesand then at 130° C. for 5 minutes on a glass sheet, and the film waspeeled off from the glass sheet. Then, this was further dried at 160° C.for 30 minutes to remove the solvent to obtain a dry cellulose acetatefilm.

[0412] Next, the film was trimmed by 15 cm at both edges, and its edgesof 1 cm wide were knurled to a height of 50 μm. The non-stretchedcellulose acetate film thus obtained had a width of 1.5 m and a lengthof 3000 m. The trimmed cellulose acetate film waste was ground, and thenmixed with non-used cellulose acetate. In that manner, this is recycled.(The amount of the recycled cellulose acetate is 30% by weight of allcellulose acetate used herein.)

[0413] (4) Stretching:

[0414] Using at least two pairs of nip rolls as in the apparatus of anyof FIG. 1 to FIG. 6, the cellulose acetate film was stretched under thecondition indicated in Table 2. Concretely, the film was passed betweenthe nip rolls while the rotation speed of the nip rolls at the outlet ofthe stretching unit is made to differ from that of the nip rolls at theinlet thereof. Thus stretched, this is an optical compensating film(phase-shift film) of the invention.

[0415] For making it absorb water before stretching, the film was dippedin water or exposed to water vapor. For the latter, the film was dippedin water at 90° C.; and for the latter, the film was exposed to watervapor at 120° C. Thus having absorbed water, the water content of thefilm is as in Table 2.

[0416] In case where two pairs of nip rolls were used, the film wasstretched in one stage; and in case where three or more pairs of niprolls were used, the film was stretched in multiple stages. In themulti-stage stretching process, the paired nip rolls were arrayed intandem, and the draw ratios in all the stretching stages weremultiplied. The resulting product is shown as the draw ratio in Table 2.In stretching the film through them, all the nip rolls were socontrolled that the film could be uniformly stretched through them inevery stretching stage.

[0417] The temperature difference in stretching the film is indicated bythe equation mentioned below. In multi-stage stretching, the temperaturecondition was the same in every stage.

[0418] MD (Machine Direction):

Stretching temperature difference=(temperature in the center pointbetween the outlet-side nip rolls and the inlet-side niprolls)−(temperature just after the inlet-side nip rolls)

[0419] TD (transverse Direction):

Stretching temperature difference=(mean temperature at both edges inTD)−(temperature in the center part in TD)

[0420] All the nip rolls used had a diameter of 30 cm. One of the pairednip rolls was covered with a 10 mm-thick rubber.

[0421] After stretched, every film was dried for 3 minutes, whileconveyed under a tension of 10 kg/m at 80° C. Then, its both edges wereknurled, and the stretched film was wound up.

[0422] After stretched, every film had a width of 1.2 m. TABLE 2 DopeCellulose Optical Acetate Number of Moisturization before stertchingCompensating degree of Re Improver Layers of Water film Type acetylationweight* % Type Film Method Content % Water Film % Samples of theInvention 11 MC 60.9 1.97 Rod 1 exposure to 4.5 3 water vapor 12 ″ ″ ″ ″″ exposure to ″ ″ water vapor 13 ″ ″ ″ ″ ″ exposure to ″ ″ water vapor14 ″ ″ ″ ″ ″ exposure to ″ 33 water vapor 15 ″ ″ ″ ″ ″ exposure to ″ 3water vapor 16 ″ ″ ″ ″ ″ exposure to ″ ″ water vapor 17 ″ ″ ″ ″ ″exposure to 2 ″ water vapor 18 ″ ″ ″ ″ ″ exposure to 10 ″ water vapor 19″ ″ 10 ″ ″ exposure to 4.5 ″ water vapor 20 ″ ″ 0.01 ″ ″ exposure to ″ ″water vapor 21 MA 57 5 Tabular 3 dipping in water 7 26 22 MC 62.5 0.8 ″1 exposure to 3 15 water vapor Comparative MC 60.9 1.97 Rod 1 exposureto 1 3 Sample water vapor 23 Stretching Step Stretching TemperatureDifference Stretching after stretched Optical in Difference AspectAtmosphere Paired Water Compensating average TD in MD Ratio Timehumidity Nip Content Thickness film ° C. ° C. ° C. Draw Ratio (L/W)(sec) %** Rolls % μm Samples of the Invention 11 80 4 4 1.45 1.1 9exposure to 95 2 4.1 115 water vapor 12 ″ 0 0 4 ″ ″ exposure to ″ ″ ″ ″water vapor 13 ″ 25 25 0 ″ ″ exposure to ″ ″ ″ ″ water vapor 14 ″ ″ ″ 25″ ″ exposure to ″ ″ ″ ″ water vapor 15 ″ ″ ″ ″ 0.5 ″ exposure to ″ ″ ″ ″water vapor 16 ″ ″ ″ ″ 2.5 ″ exposure to ″ ″ ″ ″ water vapor 17 150 ″ ″″ 1.1 ″ exposure to ″ ″ 1 ″ water vapor 18 70 ″ ″ ″ ″ ″ exposure to ″ ″9 ″ water vapor 19 80 ″ ″ ″ ″ ″ exposure to ″ ″ 4.1 ″ water vapor 20 ″ ″″ ″ ″ ″ exposure to ″ ″ 4.1 ″ water vapor 21 70 2 18 1.2 0.8 2 exposureto 80 2 6 245 water vapor 22 100 18 2 1.9 1.5 29 dipping in — 4 2 45water Comparative 80 4 4 1.1 1.1 9 exposure to 95 2 4.1 115 Sample watervapor 23

[0423] (5) Evaluation of Optical Compensating Films (Phase-Shift Films):

[0424] The optical properties of the thus-obtained optical compensatingfilms 11 to 23 are shown in Table 3. Re550 was measured at the centerpart in the transverse direction and at the two edges (of which the datawere averaged) of each film. The others except it were measured all atthe center part of each film.

[0425] In Table 3, also shown are the data of the contrast ratio and theview angle measured with the TN-mode, STN-mode and HAN-mode liquidcrystal displays fabricated hereinunder. TABLE 3 Reflection LiquidCrystal Display TN-mode Re (nx − ny)/ view angle Optical Re550 (nz − ny)vertical horizontal Compensating center edge Re450/ Re650/ (NZ contrastdirection direction Film mm mm Re550 Re550 factor) Haze % ratio degreesdegrees (Samples of the Invention) 11 138 138 0.83 1.15 1.6 0.3 25 125125 12 ″ 155 ″ ″ ″ ″ 22 115 115 13 ″ 115 ″ ″ ″ ″ 23 115 115 14 ″ 150 ″ ″″ 1.9 24 115 120 15 270 330 0.65 1.30 1.2 1.1 21 110 110 16 95 105 0.941.06 2.5 0.7 21 110 110 17 200 240 0.75 1.24 1.3 0.5 21 115 110 18 110120 0.88 1.09 1.9 0.7 21 110 115 19 83 86 0.98 1.02 1.1 0.2 20 105 11020 310 320 0.53 1.34 2.9 1.5 20 105 105 21 155 170 0.79 1.20 1.7 0.4 22120 115 22 120 125 0.71 1.20 2.2 2.2 20 110 110 (Comparative Sample) 23270 360 0.4 1.45 0.8 2.4 15 90 90 Reflection Liquid Crystal DisplaySTN-mode HAN-mode view angle view angle Optical vertical horizontalvertical horizontal Compensating contrast direction direction contrastdirection direction Film ratio degrees degrees ratio degrees degrees(Samples of the Invention) 11 8 90 105 8 125 125 12 7 80 90 7 110 110 137 80 90 7 110 105 14 7 85 90 7 110 110 15 6 80 85 6 100 105 16 6 80 85 6105 100 17 6 85 80 6 100 105 18 6 85 80 6 100 105 19 5.5 80 80 5.5 100100 20 5.5 80 80 5.5 100 100 21 7 85 95 7 115 110 22 5 80 80 5 100 100(Comparative Sample) 23 . 70 70 4 90 90

[0426] 2. Fabrication of Circularly Polarizing Plates:

[0427] (1) Formation of Polarizing Film:

[0428] PVA having a mean degree of polymerization of 4000 and a degreeof saponification of 99.8 mol % was dissolved in water to prepare anaqueous 4.0% PVA solution. The solution was cast on a band, dried,peeled off from the band, stretched in dry in the machine direction,directly dipped in an aqueous solution of iodine (0.5 g/liter) andpotassium iodide (50 g/liter) at 30° C. for 1 minute and then in anaqueous solution of boric acid (100 g/liter) and potassium iodide (60g/liter) at 70° C. for 5 minutes, rinsed in water at 20° C. for 10minutes, and then dried at 80° C. for 5 minutes. The process gave along-continuous polarizing film (CHM-1). Its width was 1290 mm and itsthickness was 20 μm.

[0429] (2) Saponification of Optical Compensating Film:

[0430] Using a bar #3, a saponifying agent mentioned below was appliedto one surface of each of the optical compensating films 11 to 23 at 60°C. After 30 seconds, the films were rinsed in water and dried.

[0431] Saponifying agent: KOH was dissolved in iso-propanol/propyleneglycol/water (70/15/15, by volume) to prepare a 1.5 N KOH solution. Thisis the saponifying agent used herein.

[0432] (3) Fabrication of Circularly Polarizing Plates:

[0433] Any of the optical compensating films (phase-shift films) 11 to23, the polarizing film formed in the above, and acommercially-available cellulose acetate film (Fujitac from Fuji PhotoFilm) were laminated in that order through roll-to-roll lamination tofabricate circularly polarizing plates. In these, the saponified surfaceof the phase-shift film was made to face the underlying polarizing film.The samples cut out of the two edges of each stretched film, of whichthe optical properties vary most significantly, were used herein.

[0434] The optical properties of the thus-fabricated circularlypolarizing plates were measured. Those comprising the opticalcompensating film of the invention all attained almost complete circularpolarization in a broad wavelength range (450 to 590 nm).

[0435] 3. Fabrication of TN-Mode Reflection Liquid Crystal Displays:

[0436] A glass substrate with an ITO transparent electrode mountedthereon, and a glass substrate with a surface-roughened, reflectivealuminium electrode mounted thereon were prepared. An orientation filmof polyimide (SE-7992 from Nissan Chemical) was formed on the electrodeof each of the two glass substrates, and rubbed. Via a 3.4 μm-spacer puttherebetween, the two substrates were stacked with their orientationfilms facing each other. In stacking them, the two substrates were socontrolled that the rubbing directions of the two orientation filmsthereon cross at an angle of 110°. A liquid crystal (MLC-6252 fromMerck) was introduced into the space between the substrates to form aliquid crystal layer therebetween. The process gave a TN-mode liquidcrystal cell (diagonal length; 12 inches) having a twist angle of 70°and a value Δnd of 269 nm.

[0437] Any of the circularly polarizing plates that had been fabricatedin the above (each laminated with a protective film of which the surfacehad been AR-processed) was stuck to the ITO transparent electrode-havingglass substrate on its side opposite to the side of the electrodethereof, in such a manner that the cellulose acetate film of thepolarizing plate faces the substrate.

[0438] A rectangular wave voltage of 1 kHz was applied to thethus-fabricated, reflection liquid crystal display. The display wasvisually checked at 1.5 V for white expression and 4.5V for blackexpression. It was confirmed that both the white expression and theblack expression were neutral gray with no other color.

[0439] Next, using a contrast meter (EZ Contrast 160D from Eldim), thecontrast ratio of the reflection brightness of the display was measured.The data of the contrast ratio in front of the display and the field ofview (view angle) to give a contrast ratio of 3 are shown in Table 2.Though the edges of the stretched film, of which the optical propertiesvary most significantly, were used for the optical compensating filmsherein and though the displays fabricated all had a relatively largepicture plane (diagonal length, 12 inches), good pictures were seen inthe entire region of the large picture plane.

[0440] 4. Fabrication of STN-Mode Reflection Liquid Crystal Displays:

[0441] A glass substrate with an ITO transparent electrode mountedthereon, and a glass substrate with a smooth reflective aluminiumelectrode mounted thereon were prepared. An orientation film ofpolyimide (SE-150 from Nissan Chemical) was formed on the electrode ofeach of the two glass substrates, and rubbed. Via a 6.0 μm-spacer puttherebetween, the two substrates were stacked with their orientationfilms facing each other. In stacking them, the two substrates were socontrolled that the rubbing directions of the two orientation filmsthereon cross at an angle of 60°. A liquid crystal (ZLI-2977 from Merck)was introduced into the space between the substrates to form a liquidcrystal layer therebetween. The process gave an STN-mode liquid crystalcell (diagonal length, 12 inches) having a twist angle of 240° and avalue Δnd of 791 nm.

[0442] Using an adhesive, an internal diffusive sheet (IDS fromDai-Nippon Printing) and the circularly polarizing plate that had beenfabricated in the above were stuck in that order to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof, in such a manner that the polarizing plate is theoutermost layer.

[0443] A rectangular wave voltage of 55 Hz was applied to thethus-fabricated, reflection liquid crystal display. The display wasvisually checked at 2.0 V for black expression and at 2.5 V for whiteexpression. It was confirmed that both the white expression and theblack expression were neutral gray with no other color.

[0444] Next, using a contrast meter (EZ Contrast 160D from Eldim), thecontrast ratio of the reflection brightness of the display was measured.The data of the contrast ratio in front of the display and the field ofview (view angle) to give a contrast ratio of 3 are shown in Table 2.

[0445] Though the edges of the stretched film, of which the opticalproperties vary most significantly, were used for the opticalcompensating films herein and though the displays fabricated all had arelatively large picture plane (diagonal length, 12 inches), goodpictures were seen in the entire region of the large picture plane.

[0446] 5. Fabrication of HAN-Mode Reflection Liquid Crystal Displays:

[0447] A glass substrate with an ITO transparent electrode mountedthereon, and a glass substrate with a smooth reflective aluminiumelectrode mounted thereon were prepared. An orientation film ofpolyimide (SE-610 from Nissan Chemical) was formed on the electrode ofthe ITO transparent electrode-having glass substrate, and rubbed. On theother hand, a vertical orientation film (SE-121I from Nissan Chemical)was formed on the electrode of the reflective aluminium electrode-havingglass substrate. The orientation film on the reflective aluminiumelectrode was not rubbed. Via a 4.0 μm-spacer put therebetween, the twosubstrates were stacked with their orientation films facing each other.A liquid crystal (ZLI-1565 from Merck) was introduced into the spacebetween the substrates to form a liquid crystal layer therebetween. Theprocess gave a HAN-mode liquid crystal cell (diagonal length, 12 inches)having a value Δnd of 519 nm.

[0448] Using an adhesive, the circularly polarizing plate that had beenfabricated in the above was stuck to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof. In addition, a light-diffusive film (Lumisty fromSumitomo Chemical) was stuck thereto.

[0449] A rectangular wave voltage of 55 Hz was applied to thethus-fabricated, reflection liquid crystal display. The display wasvisually checked at 0.8 V for black expression and at 2.0 V for whiteexpression. It was confirmed that both the white expression and theblack expression were neutral gray with no other color.

[0450] Next, using a contrast meter (EZ Contrast 160D from Eldim), thecontrast ratio of the reflection brightness of the display was measured.The data of the contrast ratio in front of the display and the field ofview (view angle) to give a contrast ratio of 3 are shown in Table 2.

[0451] Though the edges of the stretched film, of which the opticalproperties vary most significantly, were used for the opticalcompensating films herein and though the displays fabricated all had arelatively large picture plane (diagonal length, 12 inches), goodpictures were seen in the entire region of the large picture plane.

[0452] 6. Fabrication of VA-Mode Liquid Crystal Displays:

[0453] According to the process of Example 1 in JP-A 249223/2000, atransparent support was prepared for which, however, used was any of theoptical compensating films 11 to 12 of the invention. According to theprocess of Example 3 therein, a polarizing plate was formed; andaccording to the process of Example 5 therein, a VA-mode liquid crystaldisplay was constructed. In stacking the optical compensating film andthe polarizing film in this, however, the two were so controlled thatthe absorption axis of the polarizing film crosses the phase lag axis ofthe optical compensating film at an angle of 45 degrees. The devicesthus fabricated herein to have the optical compensating film of theinvention all had a broad field of view, concretely having a view angleof at least 160 degrees in the vertical direction and a view angle of atleast 160 degrees in the horizontal direction. However, those having theoptical compensating film of Comparative Example 1 or 2 were not sogood, concretely having a view angle of 140 degrees in both the verticaldirection and the horizontal direction.

[0454] 7. Fabrication of ECB-Mode Liquid Crystal Displays:

[0455] According to the process of Example 1 in JP-A 316378/1999,circularly polarizing plates were fabricated in which, however, theoptical compensating films 11 to 22 of the invention were used for thesecond transparent support. When the optical compensating film was stuckto the polarizing film, they were so controlled that the absorption axisof the polarizing film crosses the phase lag axis of the opticalcompensating film at an angle of 45 degree. Using the circularlypolarizing plates thus fabricated herein, ECB-mode liquid crystaldisplays were constructed according to the process of Example 6 in JP-A316378/1999. The devices comprising the optical compensating film of theinvention all had a broad field of view, concretely having a view angleof at least 120 degrees in the vertical direction and a view angle of atleast 115 degrees in the horizontal direction. However, the devicescomprising the comparative, optical compensating film 23 were not sogood, concretely having a view angle of not larger than 100 degrees inboth the vertical direction and the horizontal direction.

[0456] 8. Fabrication of Organic EL Device-Having Displays, and TouchPanels:

[0457] In the touch panel having the constitution of FIG. 1 in JP-A127822/1993, used was any of the optical compensating films 11 to 23.Thus fabricated, the touch panels comprising the optical compensatingfilm of the invention all had a broad field of view, but thosecomprising the comparative, optical compensating film 23 did not.

[0458] In the organic EL device in Example 1 in JP-a 305729/1999, any ofthe optical compensating films 21 to 22 of the invention or thecomparative, optical compensating film 23 was used. Thus fabricated, thedevices comprising the optical compensating film of the invention had abroad field of view, but those comprising he comparative, opticalcompensating film did not.

INDUSTRIAL APPLICABILITY

[0459] According to the method of the invention, optical compensatingfilms having a large NZ factor and having good view anglecharacteristics (especially λ/4 plates having a phase difference of λ/4in a broad wavelength range) can be stably produced on an industrialscale. In particular, in the method, the NZ factor of the opticalcompensating films produced can be well controlled, without changing theretardation thereof, and therefore the method ensures industrial-scalestable production of optical compensating films having improved viewangle characteristics.

[0460] In addition, image displays, especially reflection orsemi-transmission liquid crystal displays and organic electroluminescentdevice-having image displays that comprise the optical compensating filmproduced according to the method of the invention or comprise apolarizing plate having the optical compensating film all have good viewangle characteristics.

1. A method for producing an optical compensating film, which comprisesstretching a cellulose acetate film, the cellulose acetate film having awater content of 2.0 to 20.0% by weight, wherein the cellulose acetatefor the film has an acetyl value of from 57.0% to 62.5%.
 2. The methodfor producing an optical compensating film as claimed in claim 1,wherein the optical compensating film has a retardation value measuredat a wavelength of 550 nm (Re550) of 20 nm to 2000 nm: 20 nm≦Re550≦2000nm.
 3. The method for producing an optical compensating film as claimedin claim 1, wherein the optical compensating film has a distribution ofthe retardation value measured at a wavelength of 550 nm (Re550) of 10%or less in both a width direction and a longitudinal direction of thefilm.
 4. The method for producing an optical compensating film asclaimed in claim 1, wherein the optical compensating film has: theretardation value measured at a wavelength of 450 nm (Re450) of 60 to135 nm; and the retardation value measured at a wavelength of 590 nm(Re590) of 100 to 170 nm, and the stretched film satisfies thecondition: (Re590−Re450)≧2 nm.
 5. The method for producing an opticalcompensating film as claimed in claim 1, wherein the opticalcompensating film satisfies the conditions: 0.5<Re450/Re550<0.98; and1.01<Re650/Re550<1.35, in which Re450, Re550 and Re650 represent theretardation values measured at a wavelength of 450 nm, 550 nm and 650nm, respectively.
 6. The method for producing an optical compensatingfilm as claimed in claim 1, wherein the cellulose acetate film is dippedin water and/or exposed to water vapor to absorb water, before thestretch.
 7. The method for producing an optical compensating film asclaimed in claim 1, wherein no water film is substantially formed on thesurface of the cellulose acetate film when the cellulose acetate film isstretched.
 8. The method for producing an optical compensating film asclaimed in claim 1, wherein the water content of the cellulose acetatefilm just after having been stretched is 2.0 to 20.0% by weight.
 9. Themethod for producing an optical compensating film as claimed in claim 1,wherein, when L indicates the distance between the fixing members forfixing the cellulose acetate film when stretching and W indicates thewidth of the cellulose acetate film measured in the directionperpendicular to the fixing member-to-fixing member direction, theaspect ratio: L/W satisfies the condition: 0.1≦LAN≦2.
 10. The method forproducing an optical compensating film as claimed in claim 1, whichcomprises a step of stretching the cellulose acetate film between atleast two pairs of nip rolls by a difference in the rotation speedbetween the at least two pairs of nip rolls.
 11. The method forproducing an optical compensating film as claimed in claim 10, wherein,when W′ (cm) indicates the width of the cellulose acetate film and L′(cm) indicates the distance between the at least two pairs of nip rolls,the aspect ratio: L′/W′ satisfies the condition: 0.5≦L′/W′≦2.
 12. Themethod for producing an optical compensating film as claimed in claim 1,wherein the film is stretched in water.
 13. The method for producing anoptical compensating film as claimed in claim 1, wherein the film isstretched in air.
 14. The method for producing an optical compensatingfilm as claimed in claim 1, wherein the film is stretched in water vaporhaving a relative humidity of from 60% to 100%.
 15. The method forproducing an optical compensating film as claimed in claim 1, whereinthe film is stretched at a temperature of 50° C. to 150° C.
 16. Themethod for producing an optical compensating film as claimed in claim 1,wherein the film is stretched with a draw ratio of from 1.1 times to 2.0times.
 17. The method for producing an optical compensating film asclaimed in claim 1, wherein the stretching time is 1 second to 30seconds.
 18. The method for producing an optical compensating film asclaimed in claim 1, wherein the optical compensating film satisfies thecondition: 1≦(nx−nz)/(nx−ny)≦3, in which nx indicates the refractiveindex along the slow axis in plain of the optical compensating film, nyindicates the refractive index perpendicular to the slow axis in planeof the optical compensating film, and nz indicates the refractive indexof the film in the direction of the thickness thereof.
 19. The methodfor producing an optical compensating film as claimed in claim 1,wherein the optical compensating film has a haze value of 0 to 2%. 20.The method for producing an optical compensating film as claimed inclaim 1, wherein the cellulose acetate film contains an aromaticcompound having at least two aromatic rings in an amount of from 0.01 to20 parts by weight, based on 100 parts by weight of the film.
 21. Anoptical compensating film produced according to the method for producingan optical compensating film as described in claim
 1. 22. A polarizingplate, which is a laminate including: the optical compensating filmproduced according to the method for producing an optical compensatingfilm as described in claim 1; and at least one of a polarizing film anda polarizing plate.
 23. An image display comprising at least one of: theoptical compensating film produced according to the method for producingan optical compensating film as described in claim 1; and the polarizingplate, which is a laminate including: the optical compensating filmproduced according to the method for producing an optical compensatingfilm as described in claim 1; and at least one of a polarizing film anda polarizing plate.